Lots of good advice in this thread, I think you're on the right track with giving the Hardrock a shot until something better comes along. Ultimately though, the size will be an issue and I think you'll pass this bike along or keep it as a backup. It may be more of a problem to ride a too-large bike off road than on your commute, but that depends on the difficulty of the trails you'll be riding.

I wouldn't bother with painting it, it's a lot of work and mess, and it probably won't help the resale value of the bike. Ride it in the meantime, and you'll get a better understanding of what you want to ride next.