I want to build a proper server with room for 40+ HDDs to move my media server to and have RAID 1. I know a lot about PCs and software, but when it comes to server hardware I have no clue what I'm doing. How would I go about building a server that has access to 40+ RAID 1'd HDDs?
Depends on your budget. Since you're asking here instead of talking to vendors, I guess you want used, so just browse ebay. You can get something used like this https://www.ebay.com/itm/404093943584