Woah, 42u, that's quite something! How many of those slots are you using? What kind of cooling do you have to have for that closet, and how is the volume for the rest of the house?
I'm gonna run my private cloud merging 3 different un-backed up physical computers, and migrate services off Google.
That's my second free 42U track, but the other was mostly used as shelf space. I've got a third rack rusting in my backyard which I bought for locally for $200, originally intended to run my former employer test infra, that I brought back home after they laid us off.
I have venting into my ceiling which connects outside but I am mostly using consumer gear like Raspberry pis and Intel NUCs and the rack fully fills the doorway so volume and heat is not a real issue.