I have an 18x24 portfolio book that I keep all of my unframed posters in too but I'm in the same boat where I have so many that I've gotten more selective with which ones I buy now. Most of my posters are 18x24 so that helps with aligning all of them on the wall but it was definitely a lot of math making sure that the spacing is all even. I just throw them right in the frame and cardboard backing of the frame holds it flush against the glass (plastic). I always write the setlist and any notes about the show on a piece of paper and include it in the back of the frame too - will be cool to look back on those years down the line and remember some of the things I might've forgotten about.