The hitec digial 5645's are the best deal going in my opinion.

Of course run a 6 volt battery and here is what you get for just $50 each:
168oz / .18s

If you want to save a little more money the hitec digital 5475's are great too for about $35 each:
76oz / .18s

In your application the 5645 for the rudder would be perfect then the 5475's everywhere else would be fine. For the throttle any standard servo will work and usually lighter is better.

Just noticed you stated you already ordered the 645's, good choice.