1. There are some larger playboat designs; you may be more comfortable in a river runner hybrid; they tend to have more legroom. Maybe try the Liquid Logic CR
2. Lots of good helmets out there. I really like my WRSI
; it stays in place better than others I've tried, and you can get a faceguard for it down the road. Same goes for paddles; I have a Werner, but lots of good companies out there. Stay away from Aquabound.
3. Lots of paddle shops have demo boats you can try out. Give 'em a call, tell 'em your measurements, and let them recommend them.
4. Don't worry too much about outgrowing a boat. A lot of people start with a river-runner, then sell that and buy a creek boat and a play boat. The used boat market is pretty robust, and unless you trash your boats they retain quite a bit of value.