@Lyb You don't really have to download a whole lot to do the challenge if any at all. Specially if you have all the packs. I didnt have that much when I first started out but I really got into the CC I was finding and got a bit overboard.
But if you want to use some CC but don't want to use a lot of it I recommend starting with linzlu's tumbler. You can find a link where she has everything seperated by decade.
https://linzlu.tumblr.com
Also if you see something you like let me know and I'll see if I cant find it in my CC folder and send you a link.