i second a range finder, or at the very least, look online for the outdoor 3d tournaments and get out there. it will probably cost you 1/2 a dozen arrows by the end of your first time, but the practice in judging distance in a real world environment is the best way to practice.
I wouldnt shoot anything more than 80, and stay above 60 lbs. I have shot 60 for years and years with zero problems, i shoot target at that weight too so its nice to keep it the same year round.
80 i found starts getting to the point where its tough to get it back when you've been in a stand for 3 hours. Ive seen guys either not get it drawn back fully therefore dont get the shot, and ive seen some so wobbly that they miss.
regardless, if you shoot at a weight and practice at it days and days on end, you would be fine to hunt with it.