I would be very wary of switching the Legacy and DCC track signal feeds via a rotary switch. Did this actually work?
This is the switch I have bought. It is 12 amp at 125 VAC. The layout is 10 amp at 18 VAC, so it is under. It is also a non-shorting switch, so there shouldn't be momentary electrical contact between the positions of the switch, but it also can have up to 11 positions, so I was planning on using every other position to be doubly sure there would be no shorts, or at least put a space between the other 4 and the DCC option. Being it is a solder lug switch I have not tested the actual switch, but past experience hasn't shown it to be an issue. I also don't plan on doing live switching. It'll be set the switches, then power up the layout.
Looks like you have the Legacy base connected to the 'power' side of things. It needs to go to the common.
It is a simplified drawing, every line represents both the power and common, except the line for the Legacy base. I thought I mentioned it in the top post. But it'll either be to the track or the ZW, I'm not sure which yet. I know it'll work at the track as I have done that in a test setup. I haven't tried it at the ZW yet to see if the Legacy signal will come through the DCC booster.
Not knowing how the Legacy base would like the DCC system I would probably install a switch to isolate the Legacy base while running DCC.
As alluded to above the quote I have run Legacy/TMCC and DCC on the same track. You can read about my results in my long winded post on this thread. The Legacy system does seem rather robust and doesn't seem to mind DCC. Lionel even puts Legacy/DCC boards in S gauge locomotives (I really really wish they'd use the same setup in O.). The base isn't going to care at all what else is going to the track as it's only the common that's connected, so it should never see any voltage from the track.
DCC is in my future plans, but I currently have no experience with DCC.
I didn't have any experience either until my brother got in it with N gauge. After messing with it I decided that was the way to go when the whole ERR going away thing went down. A quick summary is The DCC booster didn't care there was a Legacy signal, and Legacy didn't seem to care there was a DCC signal. Legacy and TMCC locomotives don't seem to care there is a DCC signal, as long as there is a Legacy/TMCC signal they don't do anything when powered up (At least with the TMCC locomotives I had on hand.). Legacy locomotives mostly work fine when DCC is present, TMCC are unpredictable once they receive TMCC commands. I will be using ESU's LokSound L decoders as they have the most options for customizing sounds and can run in DCC and analog (DCC speak for conventionally.) DC and AC. So any DCC locomotives I have will not get hurt if powered up without DCC (I just need to pay attention as once they realize there is no DCC signal they will start to take off.).
Also, I am not a big fan of rotary switches either, for no particular reason though. Personal bias maybe?
I love them. I so enjoy knobs and switches and toggles and other fiddly bits. And these rotary switches have a very nice firm feeling detent, and make a very satisfying sound.