Getting the hardware is the easy part. Almost anyone can do that with enough time, dedication or money. The real kicker is the knowledge...
So unless you are fairly proficient in PHP I don't think it's a good idea to be starting your own forum hosting site.
You will need a ton of knowledge in PHP to run this type of site since you will be needing to make tweaks fairly often. (You'll have to add custom modifications to ensure things are stable, run securely, aren't glitching out, etc...)
I mean this isn't like on a single forum where you might never see some issues. When you have a forum hosting site you have hundreds to thousands of forums running on one set of code. Any issues that have 1 in a million chances of happening are a lot more likely to occur so you will have to deal with them.
Often that means making the fixes yourself (since the support forum of the software maker might have no idea what these issues are or how to counter them since the software wasn't really meant to be used in that way. And any fix they provide might take a long time.)