Yes. You can enter multiple lines of text by using | (pipe) symbol as separator or just enter 1 line, select the text and press "p", then you can add more lines (there is a bug in the last version where to enter another line you need to use Ctrl-Enter but it is ok in previous versions and already fixed in the next one).
I'm not sure if you are asking to center text lines or objects within the Sketch. You can center text by pressing "c" or selecting the center alignment option. There is no automatic centering of objects, but that's not a bad idea.
I don't understand the last question, T2Laser doesn't need the entire screen so you can just run the webcam viewer in a separate window on the screen.