How to Illuminate Standard Gauge Bumpers on a DCS System??

Lights on the track improve the signal.  Two reasons to potentially isolate them: one if you need the power they are drawing (likely not), or if the bulbs will burn out by being on all the time at 18V instead of a lower voltage from your accessory supply (I don't think they will in this case).

I have the Lionel die-cast lighted bumpers (#260's, I think) connected to track power and they have caused no problems with either DCS or Legacy. However, I have the track power to all my sidings switched and the bumpers only light when the track is powered and provide indication of track power status. 

I replaced the incandescent bayonet style bulbs with LED bayonet bulbs when I first got them, the power draw is not a factor with mine as it is very small. 

When you run conventional if the track is off the bumper is off also. I would use an insulating pin and drop a power feed from the center rail insulated track. Take a spade connector and insert it into the center rail and drop through the platform. Connect this wire to accessory power and connect this power to track common. I think the 14v pin on your Z-4000 can handle the 12 bulbs.

A Z transformer can handle a lot more than 12 light bulbs. Also all the power of the transformer can go to each channel of a Z transformer. Your KWs are the same way. Your Z-4000 is really 4 separate transformers. 2 180w and 2 smaller ones for 400 watts.

I read on another thread the Op is using a z-4000 and 2 KWs plus other stuff to on his layout.