These are not answers; just my thoughts:
1) Susan is correct; if you plan to control all your switches and accessories through command control, the DCS system will have fewer components and be cheaper overall. The AIU, for $110, can control 10 switches and 10 accessories. Lionel's ASC will only control 4 switches OR 8 accessories, for $115. For my layout, Legacy will be about the same cost as DCS because all my Ross switches use DZ-2500 switch machines which have built in TMCC capability, so I don't need to buy any ASC or SC-2 to control the switches. Additionally, I don't plan to have many accessories that will be controlled through the handheld so I don't need to buy more than one AIU or ASC for that.
2) The DCS forum has a discussion on DCS usage on a large club layout. Do a search for it and it may help answer your questions on this. Basically, those engineered filters Susan mentioned seem to do a good job.
3) Cannot answer the conventional part of the question, although if you incorporate DCS from the start the overall wiring diagram should be simpler since you can control conventional through the TIU. Legacy should not be affected by the wiring method chosen (star or bus), but the area where you have track directly over track on a lower level may need some additional grounded wires between the levels to limit signal interference.
Ron
