You should keep in mind that you are essentially allowing other users to run arbitrary code on your hardware! And Wine is definitely NOT a Sandbox, so you'll have to make sure that people don't do stupid things they shouldn't do (like stealing other peoples key files) and that they don't run the CPU into the ground (like mining bitcoins).

At the very least you should familiarise yourself with the concept of chroot, you might want to also look into the concept of containers (CoreOS offers the rkt runtime which aims to be secure).

Your math on the numbers is nice, but keep in mind, unless you are doing this with a couple of buddies you know in person, you'll have to sink time and money into this or end up with stolen keyfiles and mined bitcoins that aren't yours.