Eat 20-25 cals per pound of bodyweight, I'd start with 20 and increase it as necessary.
Shoot for 200 grams of protein.
I'd take in 60% of total calories, rely on oatmeal, brown rice, and green veggies.
Flax oil, all natural peanut butter, cashews are great fat sources.
Shoot for 6 meals a day.
BTW, remember to be patient, size does not come easy and drink 1-1.5 gallons of water.