The power/control system has been mentioned a few times. First DCC does not care whether you use 3 rail or 2 rails. It will work with either. You just have to wire you locos to pick up from the rails you are using.
Second, 10 amps should be plenty to run 2 trains at a time. My experience with O scale 2 rail models is the newer stuff does not draw much more than an amp for each loco. Older stuff can draw much more.
Third, the rule of thumb many model railroaders use for power is to run a power buss along where the track is located and put a connector drop in from EVERY piece of rail. A lot of us cheat on that but it is the foolproof way. One power connection will just not work for very long. Rail joiners will fail to make contact.
