Your front brake is your most effective brake--learn to use it in conjunction with your rear brake in order to scrub speed downhill. You're fortunate in that disk brakes are much less prone to fading and handle stopping us bigger guys so much better than rim brakes. Practice makes perfect.

With respect to going uphill, well, that too will come with practice--roll up to it at a decent clip, shift into a lower gear near the base, and spin your way up. It becomes more intuitive the more you do it. It is harder to shift halfway up.

Congrats on being out there, and good luck!