How to transition into computer science
I think it's going to depend vastly on what kind of position you want to be headed into, and how deep down the rabbit hole you wish to go. 

The one thing I would say you ought to focus on is fundamentals: No matter what kind of work you end up doing, be it programming business processes or pursuing a PhD, getting your fundamentals straight will pay dividends over and over again. Courses in algorithms, software engineering, computer architecture, each will give you a different view into the work you do, no matter where you're doing it. A CS undergraduate degree would be a good choice, especially if grad studies is where you want to go after. I understand they vary in quality though, so that's something to bear in mind.