Hi ken, you'll probably get slightly different answers to this, just because preferences and opinions vary. Here's mine.
Scale, I'm not sure but around 1/20 I think
Motors, I had a quick look at the instructions on Billings site, and was surprised to see that they show mabuchi 380 motors. Those would not be my choice for a 35 inch model. I would use 540 LN motors, the LN bit is important as these are quite different to standard ones. Low current high torque.
Speed controller, I like both component shop and Viper speed controllers. I've never had a problem with either, as long as you use them properly they just work. The 15 amp version will just do, but I recommend a safety margin and get a 25 amp type.
Battery, For normal, is not high performance models like this I suggest a NiMH pack from component shop or other trusted supplier.
You'll need matching couplings and props.
Consider putting in line fuses in the motor wires. I would.
Hope that helps a bit.