G'day Barry
Congrats on your latest purchase..
Switch wise, I have stuck the mouse switches that came with the spot light wiring looms to the dash on the LHS of the steering wheel just below the speedo etc. Really easy spot to access them. The only other switch I have in the front manually turns on 2 rear LED spots when I need to see a bit more out the back and for this I use really small 10A toggle switches you typically buy from boat shops. They are good because they fit inside the factory blanks and I have put it in the blank infront of the hand brake.
CB Wise I run the GME remote head unit which is stuck in the little recessed section infront of the cig plug sockets with the unit under the seat and extn speaker mounted to RHS of instrument panel. I always stick everything to the dash with VHB tape which saves you having to drill any holes in your new pride and joy.
I have had a 3" exhaust on all 3 of the patrol wagons I have owned. Never any overboost dramas only thing I found is that more air out needs more air in so found that for the 2 weeks I drove prior to the snorkel being fitted that there was a very noticeable lack of boost under 2K RPM. Fitted snorkel which is helping force air in and problem solved. I also run a high-flow air filter for same reason.
I use the redarc remote brake unit and have mounted the little button and led directly in front of the handbrake with unit under the drivers seat. This works a treat and is very easy to access for tweaking braking force on the fly. If you are going to drill here be sure to lift up the console and drill in the right spot though.
Same comments as others above about the heat in the engine bay and auxiliary batteries. There are after market trays which fit in there very nicely. I run a 179AH Sealed AGM Battery in the rear though as I have found over the years they don't typically like the temps under the bonnet. Most important thing with your battery is to get a DC to DC charger if you are running a deep cycle battery as typical dual battery isolater type charging systems are not capable of charging a deep cycle battery to its capacity from the alternator alone.
Hope this helps. Cheers Brad