RE: Fuel tank issue...
There is no reason not to use your Springairs. You need to check the amount to be cut off your struts as you may find there is no springing left with some struts. The recommended Robart struts for the mains work perfectly and these will work with your Springairs.
For elevon servos simply use the best possible: high torque, metal geared and digital. Rudders mini metal geared digitals.