For online sources, in addition to what others have said, tradecardsonline.com is a great resource. One source I use frequently when I cant find information online is Scrye magazine's guide to CCGs. It's a lenghty paperback volume that isn't always 100% accurate, but it's really a terrific resource for the most part. You can buy it on amazon Scrye Collectible Card Game Checklist & Price Guide (SCRYE COLLECTIBLE CARD GAMES CHECKLIST AND PRICE GUIDE) https://www.amazon.com/dp/087349623X/ref=cm_sw_r_cp_apa_POUJBbJX2VYST obviously it's outdated, but its really good for early CCGs.
(whoops this is way too old but it might be of interest)
Card City Nights (Also on Steam) is a game that mimics a CCG in a single-player app form. The game itself isn't terribly complex (indeed, it's like a ccg tic-tac-toe where you make combos on a 3x3 board), but it IS a full game in a two-dollar purchase with no in-app purchases. Plus it's just damn charming.
It won't replace any ccgs for you, but it's still a fun experience.
https://play.google.com/store/apps/details?id=air.com.pokellector.mobile
Use that app to assess valuation of singles, market changes daily so no one could really advise better than the market on day of purchase.
I'd use these and get a glass case from ikea, I have a few of the cases for my lego sets and they're pretty nice https://www.amazon.com/dp/B07F5FCSYH/ref=cm_sw_r_apan_glt_fabc_JFTP59V2D0QQFBTDWA12?_encoding=UTF8&psc=1