No need for bearing set. Glow engines are made for the bearings to be a tight fit in the crankcase. When you install the bearings, heat the crankcase to about 250 degrees in your oven before pressing in the bearing. That will expand it enough to let the bearing slide in and seat properly. You install the main bearing on the crank first, then slide the crank into the crankcase. Then you install the front bearing onto the crank and install the front end parts and tighten the prop nut quickly to seat and align everything.
Yes, all carburetors need an oring to prevent air leaks.
An OS #8 glow plug should work.