i just ordered a SRAM 7 speed cassette (12-32), partly because itīs cheap and partly because then i can have some spare room to mount the rack from the inside (or so i hope). the SRAM cassettes are cheap and i wonder why (i admit that i donīt have too much knowledge about them).
as for the brake, i like cantis, theyīre easier to adjust compared to v-brake. Xt hubs with rhyno lites make very good touring wheels, but they require a bit more work when mounting the tires.