Well to add size you want to be looking at taking in around 500more calories than you would need to stay at your current weight so depends how much you weigh now (have a look on google for some simple formulas)
As for what to eat take a look at the articles section at the top of the page for some good tips.
As for workouts without a bench then you are quite limited really however there are exercises still that you can do, and in theory you can just use the floor however is nowhere near as good as you cant get the elbows down too far and is much harder to get the bar in place, however dumbbells wont make too much of a difference bar the ROM.
Id definately suggest getting a bench if you want to train at home as allows many more exercises, as well as possibly a rack of some sort so that you can do exercises for legs and have the bar up already rather than have to clean and press it to get it above your head, although you can do dumbbell squats, lunges, split squats, SLDL et etc
Have a look here for exercises for different muscle groups -
http://www.exrx.net/Lists/Directory.html A split that you could use would be something simple along the lines of
Back + biceps
Chest + triceps
legs + shoulders
Could also pair shoulders with chest and triceps to make a push/pull/legs routine or could also put biceps with chest and triceps with back, whatever suits you really as all are completely fine.
Have a look at some of the links and articles and see what you come up with, given you a fair few starter poitns already to get you going.