HFSS set boundary condition

I want to simulate spiral inductor ,
but I don't know how to set boundary condition.
1.if I draw a air box to surround my object , how big the size I should draw ? is the size related to wavelength ?
2.when should I set perfect E,perfect H, finite conductivity , Radiation to be boundary condtion ?

I am so confused about boundary condtion .
Any experienced master , give me some hints
thanks a lot