animating in daz is pretty terrible. you can get some results with anything if you already know animation, but doing it in daz is like running blind in a forest while someone keeps throwing chairs at your legs. a much better option is using blender, but unfortunately that requires about 100x more stuff to learn before you even get to character animating.
I would advice against animations in your first game, unless you really REALLY want to make animation. just get all the other stuff down first, and leave animation for the next game.
still image renders, renpy choice menus and writing dialogue directly in renpy script file. anything more will get you in trouble you can't handle yet, and honestly won't even be worth the extra work.
gen3 vs gen8 vs gen9: what you're really choosing between are the genitals and clothes you're using, the character differences are kinda insignificant. gen8 has the worst pussy, but it's also the one you've seen the most. so if you're fine with what you've seen the point is moot. gen3 has the best pussy, but it's not really that important. 99% of your game's vibe will come from the situations you create, not from any detail.
gen3 has the most trouble with bending legs all the way up (like ankles behind ears), but then again gen8 and gen9 are only slightly less shit at that. once again the REAL choice is going blender, but the amount of learning curve is huge for a beginner.
one additional problem gen8 has is they all kinda look the same, very 'gen8-ish'. but again it's kinda irrelevant if you're fine with what you've seen already.
so in the end it doesn't matter too much which genesis you choose. the new ones have less polygons but slightly better (but still failed) topology, but once again it matters very little in practice.
for thicc milfs, 'voluptuous' slider is your friend, as is 'jaw curve' for giving that 30-40-ish round adult chin look. wrinkles rarely work out well, use as little as you can. unless you want a character looking 70yo.
but all things considered, I think you'll get most out of daz with the least amount of learning curve. unless you can draw. but if you could you wouldn't be here asking, right? daz feels daunting at first, but it's not that complicated after you've used it for a while. you'll only be using like 5% of its capabilities.
it'll always be kinda klunky and buggy and shit, and the people making it don't have the skills to fix it (so don't expect improvement), but once you find your own ways of using it you'll probably be more productive than with anything else.just start using it and you'll figure it out. we all did.
oh, one last and important thing: the choice of platform WILL decide who plays your game. renpy + daz is probably the most widely accepted one. RPGmaker or koikatsu etc will lose a lot of audience, but then again some people won't touch renpy VNs or daz games with a 10ft pole and so on.