GO WITH A BOARD ALL THE WAYYY!
I'm still a bit of a newby but i'll throw in my two cents, if I'm wrong I'm sure someone of better knowledge will correct me and help you out.
To answer your questions:
1.) I'd say everyone progresses at they're own pace. It's really hard to say. I could go down bunny hills (circles) and squares my first day on a board but I'd been skiing since I was 5. Of course I wasn't shredding down them like I do now but I made it down em'.
2.) I'd say for sure a Board, Bindings (obviously obvious), boots, gloves, goggles / sunglasses and waterproof pants / jacket. I wear under armor cold gear underneath my pants / jacket and i stay toasty all day. Just layer up and oh wear a beanie or maybe even look into a helmet!
3.)Snowboarding can be costly, especially if you don't any of your own gear. A pass at a resort can run like 40-80 bucks, not too sure about rentals (if u choose to rent) since I haven't rented in a long time. Food at resorts is usually costly so I'd suggest taking your own food. And Gas. My rough guesstimate would be like 200 bucks.. give or take a lot.
Sorry if my advice is not the best.. but I hope its some help.
Oh and last season I took one of my homies (who is the best skater I know locally) and he just could not get it. Maybe I'm a bad instructor lol but I've taken other people and taught them to at least falling leaf down a hill. I'd say if you have good general balance you should be alright. Just be patient and don't push it too hard. Don't give up, I'd say make sure you go a second time!