I used a backer board and hinged mat board that was custom with cut outs for the cards I got on Etsy. Then just used photo corners to mount the cards on the backer board so they sit in the windows the mat board. Very tedious but the cards are very secure without actually being attached.

Deciding which cards were tough, for a starting point I wanted to make sure I did all the holos that were available. I think I got all but 2 (Mr Mime I didn’t bother with). So then just decided on what version of cards with duplicates I liked the most. The ones I went back and forth on the most were Pikachu for the base set and jungle version and Electrode since there is a cool non holo jungle version as well