Unless your lights are very strong, soon you will have to get the tuberhybrida out into very good light as they are intended to be outdoor plants. I'm not sure about pinching to make them bushy, but some of mine broke dormancy in January! I had no choice but to put them under lights; I did, however, pull off a few of the new pink 'stems' and found they rooted as easily as any other cutting so I should have extra plants from them this year as well as the parent plants which are almost ready for 6 inch pots by now. I hope we are both talking about the tuberhybrida begonias . . .