GPA is good from what sounds like a good school. Two questions to ask yourself would be why do you want an MBA, and what makes sense to tell an admissions committee that fits in with your overall goal. It doesn't have to be a completely linear progression from TFA -> JD -> Law Firm -> MBA, but each transition needs to make sense, and if possible you need to work in skills you picked up at each place along the way to make your story well-rounded and unique.
I hope everyone here doesn't sound like a bunch of downers, but I will say that those that said "you don't want to look like a degree chaser" are giving prescient advice. I do agree with Method that H/S are likely out of your reach, mainly due to the factors he mentioned and also these two:
- You mentioned yourself that you went to an "OK" law school. At H/S you'll be up against people that went to primo law schools (top10) and smoked it. They probably do have spots for people with your profile, but they will be limited so they need some sort of 'wow' factor since you haven't been in the 'real world' enough to have saved it.
- Based on your experience, it sounds like you will be 30-31 at matriculation. Both H/S like to have younger classes. Not a huge factor, but yet another thing working against you.
All that said, it's not impossible if you can show that this step makes sense and build it in (maybe research the M Ed. / MBA program that Stanford offers) to your overall story.
To answer your original question, I would say 750+ for H/S, 720 for any other school (look also into Kellogg, they have a soft spot for non-traditional/meandering candidates). Pay close attention to the quant portion of your GMAT as well, since you are coming in as a 'poet,' you need a 48 or above on that section.