I will say, Elevator, Rudder then ailerons, in that order, in a small airplane like that you can use almost any type of servo, I use Jr to of the line in my 2x2 , but on my Sopt On 50 I use Hitec 5245, digitals, very very good servo ( you have to reprogram the center bandwith), if you have the servo programmer or know somebody that has one, I think that is the best option, If not, by the time you get the programmer you will be spending the same a mount of money as if you were to uy the expensive ones, I have the 821 also,but they are heavy for that application in my opinnion.

Best regards