I have been learning on my long arm for about a year and a year before on a mid arm and I am just now feeling comfy enough to do work for others--and only meander or basic panto. It takes time and practice--don't rush yourself this learning can be fun. I think what helped me the most was not working on a quilt. Get yourself a few sheets from goodwill and a piece of batting and knock yourself out.
For centering your top faster do you have center marks on your leaders? I put marks on all 3 with a sharpie as well as hints to me as to which side of quilt gets pinned to where. This way when I get the center of the top I only have to line them up with the marks. I am a very visual person so if I can see it I can do it
For thread breakage I would switch spools and see if you still have issues. Sometimes no matter who the manufacture of the thread it can be bad.
Try to enjoy your learning curve and show us pix :-)