In my opinion, maybe try draw from life rather than bases. Bases are flat and won't give you a sense of depth or proportion, so try draw from life more than bases.
Its perfectly fine, as long as the person who owns that base or picture is ok with you using it. Everyone is different and how you learn to draw can be very different than the way other people did. I myself started out the same way, tracing/using bases. I believe it helped me learn how to shape things and it was excellent practice.
As an original basemaker, I provide my resources for people to do what they like with them, tracing them blowing them up whatever, however I just ask that if you used it in any way shape or form you link back to me as your resource. Pretty much all basemakers ask the same thing.
Legally you're not doing anything bad, since you're asking permission, but artistically tracing it harmful since the only thing you're learning is how to become dependent on tracing.
The Original base was free to use is that a bad thing?