M.2 Plex Server Solution?

I was going to build a plex server with some old hardware and a standard tower, but my buddy is giving me 20 brand new M.2 drives so that idea isn't going to work. Perhaps this is too big for a mini rack, but I'm hoping smarter people than me can help me with a possible solution. I was looking at mining boards and getting several PICE expansion cards, but I'd prefer other options.