Firstimer, Stan is pretty much the man for electrical. I can tell you that my ceiling layout is double-tracked, a total of 200 feet around, powered by one PWZW, one TIU, which is powered by a RS 16-24 watt wall wart. Both lines run two engines, pulling 25 cars with no issues at all. That's a total of 100 cars up there.
Most of the guys will advise you to do it this way, for the reasons already mentioned. Doesn't have to be a RS power source. You can find a zillion online.
Jerry