Blisster, You shouldn't have any problem flying the UCD, you'll find that it's as easy to land as your trainer and a very forgiving plane in the air if you keep everything set on low rates at first.
I haven't seen anyone with the OS50 for power but one of the guys in our club is flying his with a 46AX and it flies well, it's not like having a four stroke on it but it flies pretty good. I think the biggest problem with running the two stroke is they get most of their power from high RPM's and this plane will not let you get to those RPM levels.
The tail wires won't help with the flutter. I don't have the tail wires on mine and haven't had any problems. I'm not saying the tail wires don't add strength and help stiffen the tail up, I'm just saying I haven't had any problems without them.
Make sure you seal all the hinge lines and if possible use stronger push rods. The stock .256 rods have a ton of flex and will allow the flutter if your not real careful in flight.
The stock bolts and landing gear are plenty strong enough. All the mods are being done to reinforce the fuse to prevent the block that the gear bolts to from breaking out.
I've been running Futaba 3004 servos on the ailerons and elevators for 2 years and haven't had one fail yet. I have a hobbico CS70 on the rudder.