Good questions & I'm goping to break up the post with answers for each part. I tried to avoid going too deep & avoid touching on rabbitholes of mechanics that aren't in any way standard dnd or similar so some stuff got it's mechanical relevance skirted around & other stuff you questioned below 
Also yea you can change your kit no big deal.
They all have a notable impact on your options are differing points in the game & that's one of the things making statements like "erf... you are playing an elf wizard too? Hope we don't step on each other's toes" not really a thing.
That's hardly anywhere near analysis paralysis & an effort not far from choosing a weapon in most games.
I don't think they ever presented it as rules light or anything, There is definitely more crunch, but I ran the sample adventure in the previous packet & that crunchcan be processed between turns & tended to clear up somewhere in the first session as each player learned how their class specific resource works & such. The tactical heroic & cinematic goal/tagline was nicely juggled without the usual "umm... hmm... I'm gonna... lets check how this ability works" thumb twiddling
☆ Just going to quote a line from the patreon post that had the packet...
I could be unknowingly overlooking a choice
They each carry some mechanical benefit that is going to provide a significant dash of flavor to the PC. It's really not just a box to tick. You've got to keep in mind that it doesn't have multiclassing PrCs or some kind of shadowrun/gurps/etc type pointbuy. Things like career & kits are where you find a lot of the dials & knobs that you would normally tweak through those other ways. Most of the careers happen to be split across columns & out of the two that aren't I feel like soldier needs the least understanding of system specific rules/subsystems
Also yea you can change your kit no big deal.
Yes and no, mostly no. Two of the classes mention a kit in the class itself. One is the shadow (sort of a well done blend of rogue & magical/supernatural rogue-ish stuff & the fury (sort of a barbarian) but both of those labels aren't quite accurate. With the shadow it's an ability to pick two martial kits & get the benefit of both. With the fury they are mentioned by way of class specific kits that allow them to shapeshift into a particular animal with each animal giving different badass mechanical stuff on top of the barbarian-type stuff we saw in the last packet (where it was widely explained).
Most of them have a choice or two, but it's an easy & obvious one or two. The easiest one to summarize is the elementalist, it also seems☆ to have the most choices to make needing to choose their specialty from (earth, fire, green, or void). Make the choice & you get the relevant "specialization features". After that you pick a "signature ability", those choices are debris (damage+difficult terrain), fire lance (damage+push), growing pains(damage+pull), & void ray (damage+slow).
That's hardly anywhere near analysis paralysis & an effort not far from choosing a weapon in most games.
Less complicated than you are thinking. Your class might give you one & one of those elementalist choices was an elementalist specific free strike. The basic options you add are melee weapon free strike & ranged weapon free strike, one does more damage but is reach & one has 5 squares of range. Not exactly a nailbiter decision. Your kit has some influence on those (ie raider kit adds some melee weapon damage & gives a shield bash while ward:frigid kit adds to cold damage & givres you ice armor)
Again, these are an element with a significant impact on differentiating Alice & Bob's hypothetical elf wizards from each other & will have a notable impact in play... Take what the Devil Deal & Ward (ofd royalty) gives as examples
devil deal:
Benefit: Your Stamina increases by 5 at 1st level, then increases by an additional 1 each time you gain a new level.
Drawback: When you are dying, your possessing elemental takes control of your body. The elemental yearns for destruction, causing you to attack the closest creature they notice without regard for your desires or your body’s safety.
ward:
Benefit: You know how to talk to monarchs, aristocrats,
and other wealthy leaders. When you engage with any such NPC during a negotiation, their patience increases by 1 (to a maximum of 5).
Drawback: Your royal ward regularly calls upon you for advice and takes that advice to heart—for better or for worse.
Benefit: Your Stamina increases by 5 at 1st level, then increases by an additional 1 each time you gain a new level.
Drawback: When you are dying, your possessing elemental takes control of your body. The elemental yearns for destruction, causing you to attack the closest creature they notice without regard for your desires or your body’s safety.
ward:
Benefit: You know how to talk to monarchs, aristocrats,
and other wealthy leaders. When you engage with any such NPC during a negotiation, their patience increases by 1 (to a maximum of 5).
Drawback: Your royal ward regularly calls upon you for advice and takes that advice to heart—for better or for worse.
This one is literally how does your character look & maybe give me some backstory about it type stuff not anything mechanical. Just about every ttrpg I've ever seen has this at some point in chargen. Scards tattoos & sleeping with a teddy bear are some of the examples mentioned
The example questions in it are pretty good teambuilding stuff. Here are the first two of the eight example questions, most of them in some way encourage party cohesion teamwork and/or shared history between one or more PCs.
While fighting a monster, another hero saved your life.
What were you battling and who saved you?
• In your group, who looks after everyone’s health and
well-being and makes sure that all the characters get
along? If it’s not you, how do you view this other hero?
What were you battling and who saved you?
• In your group, who looks after everyone’s health and
well-being and makes sure that all the characters get
along? If it’s not you, how do you view this other hero?
I don't think they ever presented it as rules light or anything, There is definitely more crunch, but I ran the sample adventure in the previous packet & that crunchcan be processed between turns & tended to clear up somewhere in the first session as each player learned how their class specific resource works & such. The tactical heroic & cinematic goal/tagline was nicely juggled without the usual "umm... hmm... I'm gonna... lets check how this ability works" thumb twiddling
☆ Just going to quote a line from the patreon post that had the packet...
I could be unknowingly overlooking a choice
