Richard,
The desired, differential mode signals are contained on the inside of the coax. It doesn't matter if the antenna is resonant or not. If you have proper common mode chokes on your coaxial cable, briefly paralleling the mains line with the coax, such as coming together through the area of a brick, will have no effect on transmitted or received signals nor will it induce signals into the mains line even with QRO. The lightning ground system also has little effect on this arrangement.
For the branch circuit to your shack, use 12/3 or larger wire. Use UF direct burial cable. It needs to be 18 to 24 inches underground (depending on the type of area in which it is located) if you wish to avoid additional physical protection such as conduit or concrete. With the correct type of conduit, you can be as shallow as 4 inches, again dependent upon the area.
- Glenn W9IQ