The math all works assuming your expense numbers are correct *and* you're ok with having your kids cover the majority of their own college costs, since at your current rate you'll have something like $40k in there when you pull the FIRE trigger. That, even assuming a very healthy market return over the next decade, is not going to cover 3 kids worth of college.
Note that I'm not saying you need to pay for college, I'm just pointing out that if it's part of the plan, it's a potential issue.
I think you should (you already know this) really carefully track your expenses, starting immediately. If you find that you're actually spending $85k or something, that's a problem. If you're at/under budget and things are humming smoothly along, your plan sounds awesome. In fact I'd be tempted to pull the plug earlier and find some sort of fun part time gig in your hometown if you're stressed about it. Or not - if you're only going to be spending on the order of $35-40k in RE with no mortgage... you're actually there right now, IMO. Quit tomorrow!
-W