yup, everything you just said works fine... diagram too.. keep the acr by the switch... and sure you could run the slave up on the firewall, no biggie... and charge wire to that post, as its closer than the common lug of the switch...
just make sure if the bat switch connections or acr is under the truck exposed, that you spray em with an anti-corrosive...
oh, and thats the plus of the switch, you can run in any of the 3 positions with the acr.. tho choosing a bank is the best way to go... wire a winch to post 2, run the switch on 1, everything charges, hit the acr switch for a parellel if need be, winch off a fully charged bat without touching your main bat, etc...