DaveM,
Sense you are just getting into DCS, when you purchase the DCS package, also purchase Barry's DCS O Gauge Companion book and the OGR Video Guide to DCS, these two learning formats will help you greatly as you learn and build your DCS layout. They remove a giant learning curve and help eliminate a lot of the big time frustration when building. Then always come back to get help here on the OGR forum, the people here are big time knowledgable on DCD/Legacy. I just added Legacy to my long time DCS Christmas layout and I just love it. Eventually you will probably run the dual package also, a way cool operational set up.
PCRR/Dave