RE: Servo arm length?
What kind of flying do you intend to do?
I used DuBro HD arms, cut down to one inch (servos are rated using one inch horns), and I had to reduce my throws in the radio down to almost nothing for IMAC flying. IOW, this model has HUGE surfaces that are incredibly responsive, and one inch arms will give you all the throw you can handle, except perhaps for extreme flip-flopping.
I heard about the DuBro plastic arms twisting when used with ball links. I can see that happening during violent manuevers, but since I won't be doing any of that I used them with the kit-supplied hardware- which is quite adequate for the task.
My point to all of this is that, unless you plan to really throw the plane around, you don't really need extra-long metal arms.
IMO, of course. YMMV.