For the diet aspect, id just tell you to eat 1-1.5 grams of protein for every pound you weigh. Eat .45 to .5 grams of fat for every pound you weigh. And fill the rest of your calorie alotment for the day with carbs. For example: let's just say my maintenance 1000 calories for convenience sake and I weight 100 pounds. I would eat 100-150 g of protein (4 calories/gram), 45-50 grams of fat (9 calories/gram) per day, and that would leave me with roughly 40-50 grams of carbs (4 calories/gram) per day. is Its really pretty simple.
I have personally gotten hypertrophic response in my muscles and gains in strength from training both in the 6-12 range and the 15-20 range for some exercises when all I had were adjustable dumbells at home. But id suggest going to the gym (its much easier to get a good workout in with all the equipment provided at a good gym), if you don't feel comfortable at the gym with "buff guys that look at you funny" (which is most likely your insecurity with yourself, but it's possible) then find a different gym. Try a few out and see what one you like the most. Your first step is going to be putting yourself out there for help/advice so your on the right track by coming here. But, when and if you go to one of the gyms talk to one of the guys that looks like they know what they're doing. Most of the time they'll try and help you out briefly or at least say they'll talk to you once they finish their set/exercise/session. Pick their brain a little bit, the more you learn the easier and faster your results will come as long as your applying your new knowledge and busting your a*s in the weight room.