As one note back when I was into weight lifting (while I had not known of my being transgender), gaining muscle mass was about extremely low cardio (before the work out no more than 20 minutes light jog), light stretching, and when working out, using higher weight and lower repetitions, also avoiding to stretch between sets.
So in the sense in my thinking and logic thereof of a biological standpoint and my knowledge with weights...
High cardio (warm up about 30 minutes before a work out, and another 30 minutes after the work out), stretching is key here, before starting a weighted regime get a good stretch going, as well as between sets stretch again to keep the muscles from condensing and getting blocky when they heal up, and while working out doing your exercises, you will want to do lower weight and higher repetitions per set. Also a good idea is to continue to do light stretches while in recovery mode.
I am no personal trainer but have a solid idea on the do's to weight training for both gaining pure muscle mass as well as lean muscle mass. If you have any questions feel free to let me know here, I can check back if necessary, or also send me a personal message.
Kate <3
Edit; this offer for questions about a workout regime is for anyone interested in it.