Rudder needs the most and 5645 has a lot of torque for the money. The 645's aren't much cheaper than the 5645's and servocity.com offers 15% off when you buy 4 or more 5645's so the difference is less than $10 per servo, go digital

And no, you don't need this much torque on the ailerons or elevator halves but who knows what your next plane will be???

Personally, I was thinking about a Funtana and thought 5625's on ailerons 5645 on rudder and two 5475's on the elevator halves all on 6V. But that's just what I'd do, there are a thousand combinations that would work.