I'd get a helmet. You're not going to be going fast at first but you might be falling and there's always the chance of hitting your head when you fall. I'd get goggles as well so you're not squinting all day if it's sunny and your eyes aren't watering all day if it's windy. You'll probably want some sort of ski gloves, your hands will be touching snow a fair bit so you don't want cloth gloves that'll get wet easily.

Lessons will probably start with the instructor walking you a ways up the mountain carrying your boards and teaching you the basics over a short area. They won't just stick you on the chairlift right off. Probably just rent your board and boots from the mountain to start, I'm sure they have a rental/lesson package.

As an aside, are you sure you don't want to learn to ski? I snowboard and kind of wish I learned to ski instead. Don't always have to be strapping/unstrapping a boot to get around, easier to get around on flat areas, and skis are faster.