Not sure how many a "handful" of engines is, but I think a PH180 can handle 3 or so without too much issue. What you need to keep in mind are the other power requirements such as passenger car lighting (non-LED lights take a lot of power), smoke units, lights, etc. If you are running separate loops, powering each loop with its own transformer would be better but more expensive.
Personally I would get a separate transformer, like a Z-1000, to run the accessories. Get a cheap Z-500 brick or a wall wart to power the TIU, and if it is practical power the switches from the accessory transformer.
