Topband: 80m rotatable dipole load coil questions

[Ray Benny]

I am building a 90 ft, 80m rotatable dipole. I am near the point of fabricating the inductors/coils that will go about 23 ft out on the element. I am guying the element just before the inductor. I have several questions:
1. Does the size of the gap between the center element and element tip make much difference? Is one inch enough, or should it be almost the same size as the coil length? 
2. Is there advantage of winding the coils of copper vs. aluminum? Is it worth silver plating the copper windings? I'm most likely planning to use 1/4" tubing either way. 
3. Once I figure out the total length of the element, a friend is going to run EZNEC and tell me the inductor valve I need. I will use a calculator to compute the physical dimensions of the coils. What is the advantage of building the coils on either 3 inch vs. a 4 inch form?
Is there anything else to consider in the construction of this antenna?
Tnx for your thoughts,
Ray,N6VRLocated in central AZ