It's too bad you don't have more time. It would be good to have a trial run with some of your buds so you know what to expect.
Keep the roast fat side up. It takes aprox 20 min per pound give or take. Scoring the fat before you cook looks nice when done. Try and keep your veggies roughly the same size and maybe add some chunks of onion in with them.
I suck at making gravy, so I won't comment on that aspect.
