In general I think lower bottom bracket and shorter wheelbase is what you want. Cannondale has 67mm (?) drop which I think would be fine. Might want to get some mini-V brakes, which would also allow you to use shorter stack on the stem. Good chainring combo might be 50/38 on the compact crank that came with the bike. (I'm pretty sure 38t 110bcd rings are fairly common.)

Switching from "road-mode" to "cross-mode" might be as simple as swapping out tires, and flipping over the stem.