A few things that I've needed to deal with in my off grid setup:
I like the MidNite solar controllers.
LiFePO4 batteries are great, with a few caveats:
- you must use batteries from the same batch, ie you can't upgrade capacity piecemeal, to avoid degrading the new ones
- cable lengths are important because even small differences in resistive losses between batteries can mean that one battery is doing more charging / discharging
- you can't charge below 0\*C, which I'm assuming could be a problem in New England
Not being able to charge below freezing shouldn't be a problem if you keep the batteries indoors. Is there a reason why you wouldn't? Fire concerns? Or is it just a space issue?