Getting into the minirack rabbithole

the idea is converting my desktop build into a rack mounted proxmox host.
i have a micro ITX mobo, do you thunk I could cramp it into a 10" rack or shound I get a mini ITX mobo just for that? moreover I also plan to put my 1070 ti in that build for some light AI tasks, but since I also have a spare rx580, do you guys think that I could split the pci slot in two and connect both of them? any disadvantage on this idea? (I know there could be some, first of all bandwith probably)