mcallaghan, I wear mountain bike shorts or regular cycling shorts under outer shorts. I like to have the pockets.
I am pretty new to this touring stuff, but so far I've been comfortable with up to about 25 lbs. in the rear panniers and rack bag. If and when I need to carry more than that I'll add a front carrier and panniers to balance the load. From my limited experiance I think my rear wheel will be happy if I keep the dead weight in the above range and when I've carried more weight the handling degrades.
Brad