Fresh out of a LTR, Now that I'll have more free time to myself, I'd like to make the most of it. Should I start a side business or pursue a hobby?

I'm in my thirties, if that matters. I'm aggressively paying down my student loan debt (was 90K, now 45K). I changed careers to make more money, only recently started earning over 50K.

I'm learning about copywriting. If I hone my chops and hustle enough, I could pull in some extra dough by doing this part time.

Once upon a time I was an accomplished musician, and many agree that "I got it" (or, well, had it). I have pretty much given up on music in order to tackle my debt. It would be cool to start making music again, even as an old guy.

While working overseas, I studied the local language hardcore and got to an advanced intermediate level. I love how it stretched my brain and opened up the world to me (plus, the girls!). Since moving back to the US, I haven't used the language at all and have lost a lot to attrition. It would be cool to pickup the language again.

I've got a busy work schedule and can realistically pursue just one of these. Any thoughts on what would benefit a guy like me the most?