+1 on all that. If you're in Western MA, I
heartily recommend Nick at Mount Snow Bootworks. He does an excellent job with bootfitting. Definitely get new boots first - just that will make a huge difference.
On the subject of the helmet...frankly, I don't wear a helmet because I'm afraid I'm going to wipe out and whack my bean.
I wear a helmet because during College Week several years ago, I was skiing a cruiser and found four (4) smartphones in the snow along the trail. BECAUSE SNOWBOARDERS WERE TEXTING WHILE THEY RIDE. This is not a smack down on snowboarders - it's that they are the ones who don't have a pole in each hand, and so have their hands free for things like texting on the slope. When I realized that people were texting on the hill, I skied right off that hill and into the shop to buy a helmet.
The helmet does have the advantage of being warm (most of them have a padded wool or wool-type lining). It also has the advantage of damping down the infernal racket that comes with skiing on New England ice. This item does not require an expert fit, but you should try them on because the different helmets fit different-sized and different-shaped heads. Get one that is comfy.
I would just go with rental skis until you get your feet back under you and recover from the boot purchase. I agree it probably won't take long. A GF of mine who grew up skiing Mammoth but hadn't skied on anything but straight skis came out last winter and skied with me a couple of days. I took her one run down the bunny slope to get used to them, and then told you don't pick your skis up off the snow to make turns anymore - just step on the outside ski to start the turn, pretty much - and it was one more trip on the bunny to check that out, and then we were off and flying. She could not believe how much easier it is to turn and ski now than it was on the old gear.
When you get ready to buy skis, check in with the Divas - we will help you spend your money, that's for sure!!