I've been working out for a few years now, however I've beening using a Bowflex Sport and the Bowflex Select Tech Dumbells. Now I'm about to join a gym so I can upgrade my routine. I really want to focus on squats, deadlifts, and flat bench press at the gym with free weights, and leave everything else to my bowflex at my house. I'm not really sure what weight I should start at with the squats, dead lifts, and flat bench. I max out my bowflex with all exercises, but theres a difference between the resistence amount and the weight lifting amount.

So basically I'm just wondering how I should start. I have a lot of muscle on me. Should I just start low and kind of guess and check with the amount of weight I should be using?

Stats
Wt:174
Ht: 5'7''
Age: 17