Just buy one of everything. Or two. Just kidding. Buy some extra glow plugs. On a new engine the first plug won't last to long. Also I would buy a starter motor much much easier then hand starting.
Also a battery tester for the flight battery. Very very inportant to test your battery before and after each and every flight. A quick charger would be a good investment to. That is if you like to fly all day. Also you might want a little bottle to catch the fuel that will come out of the pressure line when your filling your tank. A prop balancer is a must. See I told you 1 of everything.

Terry