For suit sizing, call the guys at Sportbike Track Gear - http://stores.sportbiketrackgear.com/
Most of their staff are riders/racers and if you tell them your size and shape, they can usually give you a pretty good recommendation for which suit to buy. They promote the Hein Gerike Celtic suit pretty heavily, and everyone on the STT staff wears them. They were able to have some influence on the design, and managed to get a back protector in the suit that's substantial enough to not need a separate back protector. They've also got a bunch of video reviews of various products, and show crash damage on the Celtic.
My husband has both the $600 Celtic, and a fully custom built $1,800 kangaroo suit - the Celtic is heavy and bulky in comparison, but it's excellent protection for the price.
If you can't get a suit that fits perfectly, call Alexa at Spyder Leatherworks
. She can alter almost any suit to fit almost anyone. (Although if you buy a size 40 suit and you're a size 52, you might have issues.)
As for trackday orgs - pick one that offers the best dates that are most convenient for you. Either STT or NESBA will get you going in a safe, controlled environment. I'm on STT's staff, and STT offers a really thorough and structured classroom and track environment for the Novice group. There's a lot of information covered and you're guaranteed to learn a lot.
If you don't want to deal with membership fees and can get days off during the week, the Blackhawk Farms sponsored Wednesday trackdays
are a good place to start too. The staff at these days are made up of STT, PTT, and NESBA coaches and CRs, along with a few racers. Good stuff, these days are a lot of fun.