I'm going to throw a slightly different perspective out there...
You want to get into programming. Your current employer works in a closely related field, but does not provide a pathway for where you want to get to.
Very few companies will take you on as a programmer just because you want to do it and you've gone to some courses. So if you want to pursue this as a career, you have two real options:
1. Find a different job that will initially have you still on the tools, working in the same type of role you currently have, but does have a pathway into programming; or
2. Do exactly what you suggest and then in 6-12 months time start applying for programming roles with some real-world experience under your belt
Option 1 would be ideal is it's less risky for you and potential employers, but jobs like that can be hard to find. Option 2 will be a lot harder on you (giving up leisure time and working two jobs) but if you have a plan and a goal in mind then the short term pain could definitely be worth the long term gain.
My company has been trying to recruit a new programmer for almost 12 months. There's a real shortage at the moment. If we found a guy who had worked on the tools for several years, decided he wanted to be a programmer, and took it upon himself to learn and get hands on experience in his own time, and had some successful projects to show for it, we'd hire him in a heartbeat. That sort of attitude shows what you're made of.
So I say, if it's what you want to do, and you're willing to put in the hard yards to get there, go for it.
As others have said though, don't forget to cover yourself. Go and see a professional and get some proper advice on insurance, accounting, etc etc. Like any other ladder, make sure you secure your career ladder before you start climbing it!
