One more thing I forgot to ask is servo choices as someone else hinted at them. At what point (i.e. what engine size and wing span) do you need heavy-duty/ball-bearinged/metal-geared/etc servos in favor over your standard plastic geared servos that come with most systems? In my case I think the largest engine I plan on using will be a .45 cubic inch.
Servo choice is normally dictated by the planes weight and what type of flying it will be doing. More torque is never a bad thing. Personally I use Hitech HS-645MG's (non-digital 107oz 4.8 volts) on all of my 60 size planes and HS-5945MG's (153oz 4.8 volts)for my 1.20 size planes. For my 40 size planes I use standard JR537 which are 40oz and also JR537's on all of my throttle connections for all of my current planes
I am moving to a 33% Edge 540 and am going with all JR 8611 servos for it at 6 volts. All of this is somewhat overkill for the planes they are in with the exception of my CG Ultimate, but I tend to like the extra margin of safety.
The Hitech servos I use claim an unbreakable gear train and I hear the JR8611 are tough as nails but you are talking over a hundred dollars per servo
Here is a breakdown of my servo use versus plane weight. All weights are approx.
4* 40 4.5lbs 3 JR537 on the control surfaces JR537 on throttle
SIG Somethin Extra - 5lbs - 4 JR537 on the control surfaces JR537 on throttle
H9 Twist 4.5lbs - 4 JRDS537 (Digital) on the control surfaces JR537 on throttle
Seagull Models Extra 300S - 5.5lbs - 5 HS-645MG on the control surfaces JR537 on throttle
Carl Goldberg Ultimate Biplane - 8lbs -5 HS-5945MG on the control surfaces JR537 on throttle
Carl Goldberg Sukhoi 26MX 9lbs 5 HS-5945MG on the control surfaces JR537 on throttle
The bigger planes all recommended at least 50 - 80 oz servos and at least 90 for high stress/3D flying.
The 33% is supposed be 22 to 24lbs and the JR8611 servos run at 220oz
All torque values are with a 4.8 volt battery installed. In all cases except for the Jr 537 and DS537 the torque values increase at 6 volts
HS-645MG :
Torque 4.8/6.0v : 107 / 133 oz. 7.7 / 9.6 kg.
Speed 4.8/6.0v : 0.24 / 0.20 second
HS-5945MG:
Torque 4.8/6.0v : 153 / 181 oz. 11 / 13 kg.
Speed 4.8/6.0v : 0.16 / 0.13 second
JR537:
Torque: 40.3 oz/in [:'(]
Speed: .25 sec/60°
JRDS537:
Torque: 40.3 oz/in [:'(]
Speed: .25 sec/60°
JR8611:
Torque: 220 oz/in @ 4.8v, 260 oz/in @ 6.0v [X(]
Speed: .18 sec/60° @ 4.8v
Sorry for the long winded post but usually seeing examples helps.