@Genstar i cant answer these as well as id *like* to, since i daily drive arch, not gentoo, but
gentoo has *really* good documentation, like, i usually hear and see it compared to arch, and the times ive gone to its wiki for something they usually offer info on how to do something for every init system it offers
as for package related woes, i feel less confident to say anything but i believe you can configure your own packages as needed? i know package management on gentoo can go quite deep so, probably https://wiki.gentoo.org/wiki/Portage and https://wiki.gentoo.org/wiki/Portage/Help would help you a bit here
the other stuff you mention like luks can certainly work on gentoo though
and, i also find myself in a similar situation with changing my daily driver, beyond it being something scary that i havent done to this extent in, 5 whole years at this point, i also just dont quite have the time to learn an entire new way of using linux that lets me safely do everything i need to do
im sure someone else could show up here and answer your questions in a more definitive way than i could right now, but i wanted to at least try for you, instead of leaving you in the dark