I'm having so many issues downloading the R3 pack it says all download limit is reached and the uncensored patch site is gone
Use the torrent instead. Betterrepack 3 have everything to play (except some new mods), no need any else patch. And it's actually better if you didn't install any addition if you don't know about it.
can someone tell me how to load character cards in the game properly?
If you use original card of the game (it only have 5 or 6 cards, I didn't remember), or the card made by yourself then there will be no problem. But if you use outside source cards (shared by other people), and get error, then it's almost impossible to fix, because that card might include mods, if you missing the mod then it can't load, for example character get bald, wrong clothes, broken legs e.t.c
The repack also got bunch of outside source cards. It's impossible to get all mods because it goes larger by date (the largest version I know is 120gb and it doesn't even have all mods), so it's common happen when some card can't load properly.
To fix it you must contact the card owner to ask them what mod is used. Or join in 4chan, discord and ask help from other pros.
what's the purpose of the illusion cards database?
In this game you can manual made your own character (change their look, outfits...), and to save that character you must save as card. The cards database have many card from other users who share their characters.