As a designer turned Marketing Agency Principal, I'd recommend going out and actively looking for job opportunities where you will learn the additional skills you require. Once you get past your first few hires, your job becomes a whole new gig. You will need to know how lots of different things work. For instance, I was lucky to have worked in the printing industry, traditional software dev industry, a design agency and a marketing agency. I got to see first hand how all of these businesses work, which has made it much easier to oversee a company that works in all of these fields. 75% of the things your business will do is already figured out and this can prevent you from having to reinvent 500 wheels . The other 25% is the part where your innovate and do something new.

Of course, there is no predefined path you should take and I always encourage entrepreneurs to follow their gut, but if you are going to get some work experience, be very strategic about it and what you are going to learn, especially If it is very specialized, such as the music biz . It definitely beats to its own drum. (Sorry, had to)