I have studied Sign Language for 4–5 years now, soon to be an interpreter. I did half face-to-face, and half online. Of course, face to face is better, but whatever fits your life and makes you study is the best!
If doing online the only way you can commit to study, then it is the best method for you! I can’t comment on StartASL, but there are plenty of online providers. The basic courses are much the same. Once you get on with your journey, then do a bit more research and be a little more picky.
I believe Gallaudet Uni offer some free, online courses