Hi Joe --
I come from a mountain biking background, and I now have a Thorn Nomad that I use for commuting, some trailing riding, and eventually (hopefully) touring. I live on the North Shore of Vancouver, which has some of the best mountain biking single track trails in the world, and anyone that I know that rides a bike has a mountain bike. I say that just so that you can put my comments into perspective.
What bars?
I have the Thorn Flat Track bars on my Nomad, and I love them. They have enough sweep back to be very comfortable, but not so much as to lose the precise handling. On my old mountain bike, I had bars with less of a sweep back, and I got pain between my shoulder blades because my elbows were out due to the angle of the bars. When you see mountain bikers, watch how far their elbows are out. That is good for control of the bike on trails, but not as comfortable. I also tried Jones H-Bar, which is the other extreme (very swept back). They were very comfortable for "cruising", but not so good in traffic, because I felt that I didn't have precise steering. It's a little hard to explain.
However, bars are very much a personal taste. Everyone has a different riding style. Don't be afraid to try something different -- it just may work for you. In the same way, what works for others may not work for you.
Will my trusty Brooks suit a mountain bike?
Absolutely! I have a Brooks B17 with a ThudBuster LT on my Nomad, and it's great for trails. I happened to ride my old mountain bike a few weeks ago, and it was very uncomfortable compared to my Nomad. That was partly because of the geometry of the bike, but also because of the saddle. I (or rather, a certain part of me) have gotten used to my Brooks, and anything else is uncomfortable.
should I go for a rigid or sus front end?
That may come down to personal taste. Don't forget that people were riding mountain bikes for years before suspension forks came along. You lose a little energy when climbing with a sus fork, but it does smooth out the bumps. If it was me, I would lean towards a rigid fork, unless the trail was quite rough. But that's just me.
- DaveS