I'd say that the more you're leaning toward fire roads and XC trails the more you're just gonna be looking at a mountain bike. Especially if -like me- you're no lightweight. Perhaps a rigid like a Surly Karate Monkey. There are things that 2"+ tires can do that you just can't get in a 40mm package. For this type of riding you probably don't need some heavy armored downhill all mountain tire, but a nice XC tire like the Kenda Happy Medium will work fine.
A multi-position bar, like the Jones Loop H-Bar, will allow many options from aero to upright, with the width needed for trails
Gears are good. I like having many choices. Whether that's a 1x10, 2x9, 3x11, or what have you, even a Rohloff.
When the fun is getting out of control, brakes come in handy. One for each wheel. Discs are kind of the go to these days, but Linear-pull can be pretty effective.
