PC Collection - Where to Start?

Hey everyone, only recently started really committing to collecting and looking for advice on the best/safest places to look for authentic pcs? Obviously album purchases and POBs when possible, where else would be good places to purchase/trade? My ult bias is Hyunjin but looking for OT8 pcs overall.

Also wondering what US available binders everyone recommends and how everyone best keeps track of their collection. Thank you for any and all advice!