Oh I didn’t mean larger like that, I meant width wise. Standard rack width is 19 inches so if it’s one of those specialty racks that’s narrower that thing I said about repurposing an old 1u/2u is pointless because it won’t fit. Doesn’t mean you can’t or shouldn’t use this rack, just that that idea is no good.
4u is fine unless you want to expand down the line. Networking gear and stuff. However if it’s a narrow rack I don’t think there will be much to put in it for those purposes? Depends on your goals. I have a larger rack but I also have my whole networking stack in it, switch, poe switch, ups, router, nas, etc.
I would consider posting on the unraid forums. There may be someone who has used similar hardware and can give guidance on how they approached the setup. The benefit of unraid is ultimately that the support community is very solid
Works from db0, congrats