I would start off suggesting that you not be afraid of lower reps. I work in the 8-12 range meaning that when the last rep arrives, it's the last one I am able to do for the set. Or, if anything, leave only 1 or 2 in the tank for that set. Occasionally, you should go as low as 6 or even 3.
Also, it's better to stick with free weights and compound movements for the majority of the work being done. As far as gaining size, remember to do slow negatives and not just drop the weight fast in order to start the next rep. I also avoid the locking out of reps during sets in order to maintain tension on the muscle and not transfer it to joints.
Protein intake as a general rule should be at least 1 gram per pound of bodyweight minimum spread over 5-6 meals a day.