22" length is about perfect length for a 308 IMO.
The best twist for 168-175s is 11.25, but there would be nothing wrong with using a 10 if that was all that's in stock. A 12 twist would probably work too up to 175s, but you probably wouldn't be able to go any heavier, and that twist works best if you are shooting 155s.
Stainless barrels typically provide better accuracy than CM.
I like either the rem varmint or medium palma contours, and will not go any lighter than these. They provide a good tradeoff between enough thickness for sustained courses of fire and keeping the rifle's weight manageable. M24/M40 and MTU are good for lengthy firing sessions, but would make the rifle's weight exceed 16 pounds.
Bartlein, Brux, Broughton, Krieger, Rock Creek, Hart, Obermeyer are all good. I have Bartlein, Brux, and Krieger barrels on my rifles; can't really tell them apart.