You're good with a 3/2 right up to January normally. Then again in May... I find that I use my 4/3 the least. I jump from 3/2 to a 5 mil in the fall/winter and then use the 4/3 in April...
And I get cold easy.
Whatever else you do, if a guy in an orange jumpsuit contacts you in re: buying one of his 'specialty boards' ... run, don't walk.
Go with the 4/3 ... a 3/2 in the fall and spring is really something that is good for the Southeast, like south of Maryland. I would recommend something like the Oneill Mutant, so you can remove the hood when the air temp is warm but the water is still chilly and you won't be doing much duck-diving. If you have a 4/3 with a separate hood, that can compromise the seal against the neck of the wetsuit, and give you quite a bit of flushing when the water is cold, reducing the effectiveness of the suit.
Volume is key!
You should get a 3/2 and a 4/3 or even a 5 if you want to go all winter. Waves are better in the colder seasons. It's worth it. If your just planning late spring/early fall a 3/2 will work. But you'll miss some good swells. I usually go till about jan with a 4/3 in jersey before getting the 5 out
North of capecod 6/5/4 with thickest boots and gloves, water temp drops to 40 in winter time. some times the harbors freeze. summer time 3/2, shorty or shorts..
If you can only have one board on the East Coast and you are relatively new to surfing get a longboard.
Yeah a 3/2 is probably not going to suffice for NH and Maine for spring and fall, unless you are a warmer person than most. North of the cape, a 3/2 should get you into November at least, maybe December. But you probably won't be able to put that 3/2 back on until May. We're well into June and water temps are still mid-50s. I wore a 4/3 a week or so ago in NH and was pretty much perfectly comfortable.