Hi.
1) Disc brakes? I wouldn't, and I have been bike touring on and off for over 30 years. Excess weight.
2) 28c is a minimum IMHO. I have been using a 27c (that's larger than some 28c tires) for the last couple years. It's the Rivendell Ruffy Tuffy and it's a real nice tire. But for touring and commuting I want a tire that gives me a flat every couple of years. I have been getting a flat a year with the Rivendells. I am replacing them with Conti TT 2000 32c.
If you can live with a few flats, 28c is a nice size. You can get tires close to 300 grams that feel lively. If you want comfort and reliability, then go larger. Although the Rivendell at 85-90 psi is pretty comfy.
3) Skip the cross frame. I got a titanium touring/cyclocross frame
a few years ago. It's sitting naked in my cellar. May become a winter bike someday. The bottom bracket is too high and the chainstays are too freaking short. Get a sport frame. That's what I use now. It's fine for light touring.