Your feedback and suggestions sound good, spell and invocation selection in particular.
I did have one idea which I hope is not cheesy. If I see the character as a herald/prophet, one level of bard might not be too much of a stretch perhaps. I am really thinking about this. Here, I could take disguise self and the equivalent of misty visions. Likewise, I could take detect magic and comprehend languages and cast them as rituals.
The shield and staff do sort of bother me. And quarterstaff is largely a flavor choice with polearm master later to make him able to fight as I am ignoring (likely) eldritch blast entirely. I want to be an ambassador social skill master who can really fight when all else fails.
I agree with you on invocations but might take fiendish (angelic!) vigor for a couple early levels only. I loses its appeal later I agree.
I am staying away from devils sight and darkness primarily for thematic reasons and resources are limited afterall too. I want to use light and later daylight if I must!
I think my biggest struggle now after seeing everyone's suggestions is the whole armor class and hit point issue. Really thinking about moderately armored level one but with a staff, no shield and questionable dexterity this is an issue. That is why I really thought hard about tomb of levistus. A shield spell could be good, and a level of divine sorcerer would be thematic, but then I am struggling to get utility spells.
Bottom line: I like the theme but it is hard hard hard to do something other than EB spam without losing most utility. As it is, there are not enough melee centric invocations!
Its a hard row to hoe.
I understand. The biggest issue with Bladelocks is that due to not having access to heavy armor, you end up focusing on 4 stats STR, DEX, CON, and CHA. Which is why the Hexblade is so popular because "Hex Warrior" gives you proficiency with medium armor & shields so you don't need strength and can focus on a DEX, CON, and CHA. Then it also gives martial weapons proficiency, so if your take human variant with Heavily Armored and focus on STR, CON, and CHA, THEN it lets you "channel" charisma so you don't need a 16 strength for combat but just 13 strength for Chain mail then focusing on CON and CHA.
Suddenly your starting with Str:13 Dex:10 Con:16 Int:8 Wis:10 Cha:16 and AC:16 or 18 with a shield …
but that doesn't really fit your concept.
tomb of levistus is a once per short rest ability, so
your not going to be able to rely on it for anything more than an emergency save. It takes you out of the fight next round which give everyone a chance you heal you but you can't move or heal your self while incapacitated so if the enemies just wait they can kill you next turn if your really close enough to death to use it. At that point your using your action do delay your death one round INSTEAD of damaging or killing the enemy attacking you. IF enemies leave you for other targets, your allies heal you before you head back into combat, and/or your allies can kill them on what would have to be the last turn of combat... then sure its good... but that's pretty … niche … in my opinion. It's also less useful at lower levels when your more likely to one shot enemies or be one shot instead, your allies healing spells don't recover you much, and the temporary hit points your getting can be wiped out before your next turn killing you in your iceblock anyway meaning it just wasted your turn. Fire spells do double damage and are pretty common so that could be a problem too depending on enemies. At level 9 however your getting 90 temp hit points so unless your fighting a Red Dragon, Fire Elemental, or Demon it should work pretty good. I really think this spell is week (possibly just a bad choice at level 5) to start but gets stronger the higher level you are (lvl9+ its a solid pick... maybe level 7 … in my opinion, the difference of 20-40 more hp then is significant).
"Angelic" Vigor is ok but it doesn't stack with Armor of Agathys which damages enemies that hit you as well so I would consider it better. You can use it on turns after you lose Armor of Agathys but because your recovering your spell slots on a short rest you will likely have Armor of Agathys every fight adding to your damage and defense. Anytime you cast "Angelic" Vigor on later turns to increase your health your losing a chance for damage. At early levels your likely to kill one enemy per turn so the trade off of losing a turn adding 5-8 temp hp vs killing an enemy that does 5-8 HP the turn you cast is seems like a lose to me when you could have prevented the same damage and be one enemy down by just attacking instead. You can't get it until level 2 and at level 3 Armor of Agathys increases to 10 temp HP and damage increasing its effectiveness.
Keep in mind you can re-skin Armor of Agathys and change the damage per DMG to something relevant like radiant then alt level 3 two week enemies might die hitting you. I understand the draw … I just personally believe it looks good but in practice "Angelic" Vigor is a "trap choice". If you feel a need for "Angelic" Vigor thematically I understand but then I would recommend dropping Armor of Agathys for
Charm Person which might fit your herald design a bit more. Also, Charm person has an interesting side effect defensively people over look. If your group focuses on a single target you can charm a second target attack you. It can freely attack your allies but it can't attack you its hurt by an ally and makes its save. If your allies are ranged and 40ft away it means at the very least the target wastes a turn. I also like it for defense against in party pvp and charm effects. For example, a vampire charms an ally and says "fight for me", you charm ally and attack the vampire. The Ally IS charmed twice and the stronger charm only overrides if their is conflict. Vampire charm has no spell level as an innate ability so again your ally will not attack you and must run off to find a valid target giving you and your range party members time to kill the vampire without having to kill your charmed fellow party member.
I think considering combat initiation aspects of invocations Mask of Many Faces or One with the shadows may help you find invocations that while not "melee centric" still have viable combat applications. Consider that hiding in the shadow of a tree that cast across a road or looking like an ally would allow you to get in melee range on round one and could mean two additional rounds of engaging in melee where you might be otherwise running 120ft to close the gap on range opponents and perhaps even a third if you get a "surprise round" which is not technically a thing but if enemies are under surprised condition, realistically is. Early rounds matter the most particularly at low levels where your dropping bodies every round and spending those trying to get to the enemy so you can engage in melee to begin is a huge combat loss. I think consider utility spells that deal with that instead of attack from range will do you well since your design is going to be heavily built for melee and not being in melee means that is all waste...
I am curious what your current planned picks for level 2 invocations are?
Multi-Classing divine sorcerer or bard would be fine, Warlocks multi-class well but I would avoid doing more than a single level of one until after level 9 warlock because it will slow your progression and your getting the most bang for one level of full caster. Divine Soul Sorcerer's "Favored by the Gods" would be good for a fighter but it begs the question, why the angry angel is your patron if you already have divinity in you blood? If its imparted to you as a gift from the patron I guess but it seems redundant to the warlock abilities the patron is already giving you... Bard Collage of swords would give you medium armor and you can use your quarterstaff as focus for your bard spells. Despite its name its not dedicated to sharp pointy weapons and works well with the idea your training to fight melee, learning arcane, and if after level 9 you wanted to grab a few more levels Dueling fighting style would add +2 damage to your staff as your only weapon if your using a shield (you might convince your GM to let two-weapon fighting apply to the but end attack of polearm master) and the +10 speed with Flourishes at level 3 bard would all be mechanically good while being fluffy with your herald/prophet who fights in close combat... That's again just my view on it.
Regarding shields and quarterstaffs... Bucklers are actually used with spears … I couldn't find anything IRL for quarterstaffs
http://wiktenauer.com/wiki/Gladiatoria_group
I did find this as a visual on my previous stated idea... I might have made the shield smaller though, block with the shield twist for the strike. I do HEMA and can see how this could work. Using sword and shield its not uncommon to engage the weapon with a shield then strike while the weapon is bound. you would just have more power for binding the enemy weapon and the attack would be a twist perhaps predictable vertical strike. Also, not good against other shielded opponents because of the angle of attack favors the enemies shield.
