I am not sure exactly what your goals are but it seems you want to put on some size, the 10-20 lbs you mentioned, and that you want it to be lean muscle. So the first thing you need to do is keep your protein around 1.5 grams per lean body weight.

From your post it seems that your only doing pushups and some dumbell curls, so you are only lightly working your chest and arms. This isn't going to be very successful for putting muscle and weight on you. You want to have a full body workout which means you have to do every parts of your body (legs/back/shoulders/chest/bis/tris/abs/etc.) so you will have to pick a major muscle group or two and assign a day to work those muscles. If you look around on the board you can see some good sample routines and there is even a post which lists exercises to target specific muscles. Doing just those exercises you have listed will be good for just toning those areas.

I know you said you don't want to get a gym membership but to be honest, there is not a whole lot you can do with dumbbells. Adjustable dumbells are a great addition to a home gym, especially for a beginner who doesn't need much weight. But you will soon learn that your 30 lb dumbells will be obsolete in no time. To fully work your body and put on some size/weight your going to need at least a decent rack and barbell/plate set in addition to your dumbells. It would probally be easier for you to use the college gym, trust me alot of the people there are more out of shape than you expect and they tend to have decent equipment their for the athletes.

So you can see that your going to need to do more than just taking in more protien and doing curls/pushups to put on weight and size. You really need to do some heavy exercises and therefore you need to get to a gym or buy some real equipment if you want to see real benefits in a month.