Check out this, this & this for themes.
Go for an arcade, a shop may be worth it as you could offer gaming services, such as gaming maker et cetera, thanks if I have helped.
As much as I think that there are much more advanced options than phpBB, here's one mod I really suggest you should check out. Many of these guys here don't use it, but it's really useful.
As for other MODs on phpBB, the only thing I can say is look through every mod there is on the site and see what might work and what won't. It takes a lot of time to properly run a forum.
Try to find a theme that isn't like every other phpBB forum out there. Somehow, the vast majority of phpBB themes stick to the same, traditional structure. Your potential members will be impressed by an innovative and fresh style.
I agree with Zane. I'd even go a step further and say.. don't look at those templetas at all and make your own style! Its really not that hard if you know a little CSS (and HTML).
