I agree with what you are saying about getting it right Paul, if you can juggle the 2 jobs then why not, particularly over the winter months, then see how you get on next year and if you still like doing it etc. You can then jump in like the guys are saying if its viable for you.
Only thing I don't agree with is when you say you are no "spring chicken" I thought you was going to say late 50's or early 60's etc.

Im just 48 (in October) and im fit as a flee (for my age anyway) I still train 3 days per week and certainly don't feel like im getting old (older maybe like we all are) but not old. Your age is nothing if you keep yourself fit, this job will do that for sure. Sitting behind a desk every day will make you fat and feel old for sure!!!

Good luck with it mate.
Cheers
Steve