Size can be important in Rugby depending upon the position you play, but its not as important as most people make it out to be, especialy this early in your career. "Ooh he's big I bet he'd be good at rugby(or insert any other contact sport)". Not necessarily so, if they don't already have a tactical understanding of the game and how they fit into it.
I can't count the amount of runners, fighters, footy players etc who look like they would be awesome with big muscles, or a huge squat or bench numbers but are actually really crap at there chosen sports, being beaten by fit, but rather average looking but technically good practioners.
Get good first, really good at the basics of your sport including natty lifting for at least 2 more years, then maybe consider adding PED's, to keep up with the best. A sportsman is a finely tuned machine, so remember to leave your best performances for on the field and not training in the gym.
You have actually only just entered the most profitable time of your life for natural training, natural testosterone levels should be sky high. Even though you probably won't grow much taller, your bone density, and muscle mass are going to increase with the type of training you will be doing.
By all means talk to your friends who are on the gear, find out what they're doing. Just keep in the back of your mind, how many of them will actually make it to the professional levels.