The general thing is that, assuming you actually install it correctly, kplug is a super powerful mod that revamps a bunch of stuff and adds a lot of cool new features/poses and a lot of other things, but it changes how the base gameplay is (as in when you're doing 'interactions') that it will likely cause some misc issues. The first time I dabbled in it I wasn't a fan of the first person mode and other things (though as people pointed out you can change that from a menu, my game was bugged and it seemed to not happen again after I closed/reopened it even without any changes), but many people here like
alex2011 have a lot more experience with it. Heck, the mod is so good/powerful, apparently the creator of the mod is now hired by Illusion because it's so much work and effort put in. The fact that it changes as much as it does (like allowing you to be in a room with like, 3 girls, then just swap focus or invite new people in while others are having sex in their own corner of the area) is impressive.
*might as well ask because decided to actually look up cards on the booru: how exactly do you download them there? Do you just save the image as a .png and move to the appropriate folder? How does the game even know what's a character card and what's just a random picture?
Copied from random booru image since apparently mods may matter:
To check the necessary mods, download the Koikatsu card, then load it on this page "
You must be registered to see the links
"
so a list of the mods used by the Koikatsu card will appear, in addition to the links to the source to download them.
*also looking at some of the furry mods of like, hooved characters, it does seem that a lot of mods that really change bone structure may not be in the game. On the Booru a lot of them seem to have the creator say if any mods are required, but the mod listed in this one I can't find in the RX4 pack:
You must be registered to see the links
and the stuff required to get this character to work seems... like a lot of work
You must be registered to see the links
(just noticed that both of those are not Koikatsu cards as well so that might explain it as well, so also look out for that)
So if you want to just make a catgirl that looks like a human with ears or maybe just want to made like a Sonic OC then you might not need anything fancy, but if you are planning on creating/importing a bunch of furry characters, expect downloading some mods first. Also I should point out that any mod that deals with the character models and 'bones' will likely cause some wonkiness somewhere. Kplug has issues with some mods to the point that it's better to disable the conflicting mods for it to work, but even without kplug don't expect everything to look super nice. I remember doing the drag+drop thing to create a futa character and they were a different height than the male default and every time they took part in sex the penis was not positioned correctly for the act (i.e. vaginal may have it sticking out of the pelvic area, and not in a sexy way), so just... be advised that RX packs are a really good baseline pack, but once you start diving into other mods you're on your own.
