Robert,
Welcome to the OGR forum, lots of good people here who can answer most all your questions. Before you start building your layout wait for your DCS O Gauge Companion book to arrive, it will save you a lot of time and grief. 2nd pick up
the OGR DCS Video Guide and watch it, Rich does a great job with the video, especially if you are just starting out in the DCS world. These two purchases I always recommend to all new runners.
Further I highly recommend you run your trains on the required dimentional curves
the train instructions calls for. Many times it is possible to run on shorter curves
however you are just looking for engineering trouble doing it.
Good luck with constructing your layout.
PCRR/Dave