I agree about taking the job, and also want to second the thought that your new employer may be willing to subsidize the cost of the degree, or at least to tweak your schedule so you can do both at the same time. And it does make sense to work in a school first and see how you like it, before doing the degree, though you should keep in mind that one school is not all schools; the people and the culture matter a lot.
Having summers off every year for the rest of your life is HUGE, and in my opinion worth a lot of money. That being said, have you looked at the market for the job that degree would qualify you for? Being in this new job may give you access to a lot of information you can't easily get--inside tips on what the market is like, for instance--but I would start trawling the boards that advertise that kind of job and do what you can to figure out, for instance, how big the applicant pool is, whether you realistically would have to consider moving in order to get the job, etc.