Multiple Topics, one forum, bad idea?

[محروم.كوم]

Hi everyone, I am new and am wanting to purchase vBulletin because It seems like the best after my extensive reviews. I am involved in a few big things, well big to me And I would love to have a forum community involved and active on my sites.
I was wondering about having one forum, but with a few sections, each area with different main topic, such as computer repairs, and audio/music producing, and some Church projects, would be my three main categories.

Is it a stupid idea to try something like that, should forums be only about one thing only?
Just cant really buy 3 licenses, thanks for your input. __DEFINE_LIKE_SHARE__