Randy, down the street from the Big E, are the West Springfield yards of NS or CSX(used to be B&A/NYC/PC/Conrail). Don't know if its walking distance in January, with a 6 year old, but if 'Grandpop' is coming along, maybe he can do that with him, to give Dad a break. There are plenty of operating layouts at the show, for 'shock and awe.' FWIW, my first visit to this show was 3 years ago, and the breadth of what was on display, and/or for sale, was virtually beyond my comprehension, leaving me at 48 years old feeling overwhelmed. This time, I have some idea of what to expect. My 'visit strategy,' this time is to look for particular things, and companies who's products I'm interested in, and to try and not get caught up by the mob scene, or movement between buildings.
The photo of what you've got so far, looks promising. 15" radius for an HO layout is on the tighter end of the spectrum, which if you keep it, will work best with short cars, locomotives, and trains, both in general and as a group.
As for your question about the ability to run DC and DCC equipment on one layout, and how to wire it, my advice is as follows:
1) Yes it is possible, with some or all DCC systems. To some extent its o matter of whether to hook up the DC powerpack, or DCC powerstation and 'loconet,' to the track wires.
2)You might focus on trying to get your questions answered at the show, by someone with better knowledge/experience than me with this issue. I am currently building a layout myself, and am comtemplating going to DCC, for better or worse when I get to that stage of construction/progess. Remember, its a mob scene at the show.
3)might ask over in the 'Electronics/DC/DCC area of the forum, as there all ready may be some threat that has previously addressed this issue/desire, and or, can do so for you, if you post a new thread, there, or continue an older one.
Its late here, I'll probably be to Springfield toward the end of today, or Sunday. Its a 3 .5 hour drive for me each way.
Otis