B'anyway, you wanted feedback on what you have so far...So, let's see...
As I've already told you, I do not believe classes should be created from the ground up with feats and multiclassing assumed....but since this is a homebrew/for your use...obviously you know that those are in play and even intentionally want this to be something people MC out of.
On the overall, it's solid but there are a few items that seem overpowered and others that seem unnecessarily/arbitrarily constrained to me. Mostly in the higher levels, but we'll get to those.
Uncommoner
Prerequisite: No ability score over 14
HD: d8
HP at 1st level: 8 + Constitution Modifier
HP at following levels: d8+ Constitution Modifier
Proficiency
Armor: Padded
Weapons: 2 simple (1 may be ranged)
Tools: Any 1 (except Poison, Disguise, Forgery, Thieves)
This is all fine up to the Tool prof's. Just a details/possibilities qualm for me: if they can have Alchemists tools, Healers and/or Herbalist kits, why are they prohibited from Poison Kits or Thieves' tools? They're more specific skills that need some practice and intense training...but surely no moreso than Alchemy or herbalism. Those require an INVOLVED amount of knowledge and study. A guy who has worked in a locksmith's shop or just tinkered around with small picks or plates, figured out how to "pop" things open. I guarantee you anyone with ANY kind of herbalist training/tutelage is going to be taught what is poisonous!
I say, just make this "Any 1 set of tools or kit", without exceptions.
Saving Throw: Constitution, Intelligence
I'm inlcined to make this one or the other...or, for that matter, ANY single ability of their choice.
"But all classes get two Save proficiencies" you say? Yes! But these guys are "Uncommon" and no other class gets to CHOOSE their save prof. [This also lends a bit of impetus for your players
Skills: Any 3 of Athletics, History, Religion, Animal Handling, Nature, Insight
Another quibble here...Religion, Nature and History all involve a good amount of study/learning. Uncommon, yes. But I think a bit "esoteric", maybe for uncommon Commoners, certainly to have skill in multiple esoteric areas. I might swap out Nature, at least, for Survival...and Religion for...I don't know Persuasion? I suppose you could leave the rest.
OR, as with the skills, just open it up. These are supposed to be uncommon guys from any/all walks of "normal" life, right? Give them 3 (I might even say only 2), but they can choose whatever ones they want...as befits the characters backstory/commoner experience.
OR, if you want the skill "list" like other classes have, then I'd go with: "Athletics, Animal Handling, Insight, Survival, and/or any ONE Lore[Int] skill of your choice. Your Uncommoner may only ever have a single Lore[Int] skill."
Equipment:
a) One of each weapon known. If no ranged weapons are known they also get padded armor. Ranged weapons get 20 ammunition.
b) An extra known thrown weapon, if known, or a Healer’s Kit
c) An explorer’s pack
d) The known tool/kit
As written, this sound like you're getting a third known weapon (if it's thrown). I would probably reorganize Equipment thusly:
a) One weapon known and a) a ranged missile weapon known w/20 ammo or b) two ranged weapons known if they have the "thrown" property or c) a second melee weapon known.
b) Padded armor
c) An Explorer's Pack and Healer's Kit
d) The known tool/kit for their chosen proficiency.
Multiclassing
Proficiency granted on multi-classing: a single simple weapon, 1 tool/kit (excepting Poison, Disguise, Forgery, Thieves)
I'd take this out. There is no precedent for a class giving specific directions/changing what they grant (let alone granting EXTRA!) for multiclassing. If you multiclass from Uncommoner to some other class...you gain the proficiencies of that new class. YOu don't get MORE from the class you're leaving. This is bad (and I'd say OP), take it out.
Uncommoner Features
1st level: Expertise in any one skill or tools known
Unusual (the Uncommoner has a Feat, if human this is a second Feat)
Expertise on 1 thing is cool (if a bit underpowered), matches the idea/theme/flavor without stepping on Thief toes.
I've already said about the feat...but this additionally assumes the use of the Human Variant (for their extra feat). This is a no, for me. I LIKE "Unusual" as a feature name...but it shouldn't depend on picking a feat [obviously, it
can because this is a homebrew. But I do not believe it
should.].
2nd level: Helpful (the Uncommoner is able Help as a bonus action)
Militia Member: 1 Polearm (glaive, pike, and halberd) or 1 ranged simple weapon
Helpful is a GREAT idea! I might even make it a 1st level trait...push the expertise back a level or two and you can just let it be two skills/tools, as normal/the Rogue.
Militia Member grants an additional weapon prof? I mean, I get the flavor and it makes sense...but...meh. I guess it's fine. Leave it.
3rd level: Choose an Archetype (Factotum, Expert)
4th level: ASI or Feat
No "or Feat." ASI is the feature. If a given table is
using feats, then the option to pick a feat instead is on the table automatically and a feature of gameplay, not the class.
5th level: Proficiency in Light Armor
New Career (the Uncommoner takes a new background as if a 1st level character)
Work Together (the Uncommoner is assumed to be skilled when helping another character complete a task)
Coupla things here.
1. Why are they receiving 3 features at 5th level? Classes are not built to gain more than 1 new feature in levels higher than 3rd (for the most part). In a few instances you can have a low level feature grant additional abilities/uses at higher levels with a new feature. But shouldn't be the norm and definitely not "get three whole/new features in a single level.
2. New Career. Again, I get the flavor/what you're trying to do, but selecting another "Background" (and all that entails: bonds, flaws, ideals, more skills, etc...) at 5th level just hurts my immersion brain.
3. It seems to me proficiency in armor (particularly Light which they already have proficiency in one of) should be coming before proficiencies in additional weapons.
To be honest, I am tempted to take the Padded prof out of the base class at all. Make "Armor Adept" [or some such] a thing at 1st or 2nd level: "Choose ONE kind of light armor in which you are proficient. At X (slightly higher) level you learn another Light armor of your choice that you have access to. At Y [a third, higher] level, choose a third light or any single type of Medium armor, you have access to, in which you become proficient.
4. Auto prof to any skill for Aiding Another seems OPed at 5th level. And you have too many features here anyway.
6th level: Archetype
7th level: ASI or Feat
8th level: Shield, 2 weapon proficiencies with no limits
Huh? So they get proficiency in Shields now? I would add that into the base prof (Padded and Shields) or, if you like the armor adept idea, include it in there, giving them shields with their 2nd light armor choice.
And two more weapon profs? That brings them up to 5? Why not, as the PHB models, just go the Monk or Rogue route and say they get all [can be proficient with any] Simple Weapons, and X martial weapon...in this case, given the early level and weird specificity, just add the polearms there. If you want/the intention here (as I suspect) is to add in Martial Melee weapons...then just do that as the 8th level feature.
Or, so as to avoid "You are now really a full-fledged Fighter", something like, "Student of Arms: you become proficient in a martial weapon of your choice. For each level after 8th, you learn proficiency with an additional 1 martial weapon, up to a total of 1 +your Int. modifier (or something like that)."
9th level: Archetype
10th level: ASI or Feat
11th level: Rally (with 10 minutes of speaking the Uncommoner can grant the benefits of Inspiring Leader, or can give half their level + Charisma modifier on any skill/tool/kit check)
New Career (the Uncommoner takes a new background as if a 1st level character)
I am really not a fan of granting Feat level powers as class features. If you want something like this, duplicate or adjust the Bardic Inspiration mechanic to do something akin to what you want.
See above regarding taking on new Backgrounds at these levels. If the object is to grant additional skills, seems these places are where you want/ought to have your Expertise to boost the bonus to the prof's you already have.
Not to mention there is no way/reason you should be receiving two new additional features at 11th level!
12th level: Archetype
13th level: ASI or Feat
14th level: Most Skilled (all skill, tool and kit checks are conducted with advantage)
Most SKilled is a good feature. Flavorful and makes sense mechanically. Might even be a bit too far back. THIS could be a nice 11th level feature. Scrap the ones that are there.
15th level: Archetype
16th level: ASI or Feat
17th level: Swarm of Workers (if intelligent neutral or friendly creatures are within a day’s travel a number equal to 4d6+Charisma modifier will answer the summons. They obey for a number days equal to a Persuasion (CHA) check. They will not fight, but will work for you at half wages and can provide cover. This increases to 5d6+Charisma modifier at 20th level. If no available creatures are in range 2d6 Unseen Servants are summoned and disappear in an hour)
Annnnd ya lost me. Some random neutral or friendly folks, within a DAY''S travel are going to just SHOW UP? How if this guy "summoning" them? For half wages, no less...and "can provide cover"?! So, call these guys up to be cannon fodder?! This is just plain wrong. A number of days equal to a Persuasion check...how many is that? What is the check/DC?...don't even get me started that Unseen Servants now magically appear.
Just no. Drop this. Or try to rewrite it from the ground up...but I suspect it will still be a no go, in my mind.
New Career (the Uncommoner takes a new background as if a 1st level character)
Again, nope. See above.
18th level: Archetype
19th level: ASI or Feat
20th level: Rush the Job (any long term activity can be completed in one-third of the time listed in the downtime activities)
Why 1/3rd? Seems just 1/2 is just easier. Also stipulate that the use of this feature does not stack with any other downtime time shortening features or abilities. So, it's not like if you have some way to do something in half the time already, the Uncommoner can do it in 1/4. Nuh- no.
Ok. I need to get on with my day. So I'll come back and go through the subclasses later on. Overall, like I said, good start/restart. But a few areas I see/think need work and some reorganizing.