Would an online writing skills practice improve my writing skills?

Yes, of course. Unless you only want to settle for mediocrity and don't want to put your work on the front page of SERP, an online writer should always be mindful of how to present his/her stories to maintain or increase traffic.

Certainly!  It would also give you the courage to self-examine, face criticism and assess your strengths and weaknesses. And provide you with state-o-the--art expertise, too.