Re: New to this
Welcome Scott. You've come to the right place for answers.
As far as sprocket size (diameter & tooth count) it will depend on what engine you plane to install. Typically speaking if you're looking at the Chinese 2 stroke you'll want to go a little larger sprocket than what usually comes with the kits. Think of sprocket size as gears in a transmission. The larger the sprocket, the lower the gear. 44T sprockets are somewhere in the middle of the road, 48t is a little lower gear and then you can go crazy with a 56T or larger but don't expect too much in the way of top end speed.
Guys who are looking for speed will go down to a 36T and in some casese 32 or even 28. They have to pedal like crazy to get moving but their top end is good and engine RPMs are low.
You can check out the "laws & Legislation" section for answers about legalities in your area.
Like Silverbear suggested, start reading and see what is available in the way of powerplants for your bike.
Above all, have fun and ride safe.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"