Lionel PE,
As you can see by this thread most of us eventually purchased both systems, because we like both type engines. In my Engineering opinion it is easier for a runner to first set up a good DCS layout, and then add legacy to it, than the other way around. As far as the DCS wiring goes, if you use the correct discipline while building your DCS layout, you will never really have a problem, this is where Barry's DCS O Gauge Companion book is so great. His exacting written instructions are just fantastic, and he covers how to add TMCC/Legacy to the DCS layout. IMO Marty F maybe the foremost authority on DCS/Legacy layout building, his experience level & knowledge is just outstanding, and he participates here for you to ask questions of, he has always been very helpful to everybody. Marty E is the Legacy man, his knowledge is like Marty's F's only on the Legacy side, he participates on the OGR also, and is willing to answer all our questions. There are others of us who are very knowledgeable also, and we will help you as much as we can, when you decide to add command control to your conventional layouts.
Merry Christmas!
PCRR/Dave