The metal rod is ok as long as you break electrical conductivity at the ends with plastic or nylon clevises or links.

You can use the same type of switch for the battery that you use with the radio.

It doesn't really matter where you put the ignition module as long as two things remain constant, the second of which is extremely important with 3W. Number one is that the plug wires have to reach the plugs. The second is that a 3W ignition likes very much to be kept cool, so pay attention to cooling air and the mounting method. Other than that the location doesn't matter.

Not a very good idea to place the ignition next to the receiver, so keep a little (as much as possible) separation there.