your 690 woodies will be ok for learning with.
those servoes will run fine at 6 volts, but make sure you have a step down for your tail servo. they are not the fastest or most powerful servoe's. i would upgrade them to something like the 5452's once you want to start throwing that thing around.
stick with the aluminum frames for now. they are very strong and relatively crash resistant. the carbon ones save you some weight, but thats about it.
for crash's. your generally looking at blades, anything on the rotor head, tail boom and its torque tube (if you get a boom strike), and landing gear. it it all depends on how you crash.
you should balance the clutch and fan assemblies.