After you come off your cycle, holding on to your gains is going to depend on diet and how much you burn through training. If you want to build muscle, I would stay away from cross fit. That type of activity will make a big guy get small. Stick with training every body part 1x, maybe 2x wk. 

Sounds like you picked some good gear. Just remember that a lot of what you initually gain is going to be water, in the muscle. It isn't real muscle. Once you come off, this water will flush away and you will be left, several lbs lighter. Thats ok. The fluid will have helped you reach your goal of gaining muscle. The scale weight while on, was not the best way to range, as to how much new muscle you gained. Look at the scale 5-7 wks after coming off and that wil give you a decent gauge. Better yet, have your body fat tested so you can check to see how much lean muscle you actually have.