Good to see league supporters getting involved in the refereeing ranks.
You are to be commended for being willing to give it a go - just don't cop any rubbish from people. The abuse will come (been there, done that - but league's abuse will be greater) - but patient and sensible referees who stand their ground without being a Nazi with a whistle will earn respect.
I know a few league referees, and I've also had the pleasure of meeting one of the NRL's most prominent refs - they all say that it is tough starting out. League and AFL have one of the highest referee turnover-rates in all sports - something 50-55% of all refs give up in their first year.
If you start, then stick with it for a while - set yourself the goal of commitment to the job for 2-3 years - perhaps longer. Set other reasonable goals - like making a particular grade, or specific areas to work on like communication and fitness.
But above all - have fun, it's just a game.