Whole project looks great !! But since there are so so many posts I'm not sure if this has been brought to your attention:
Looks like you have employed Atlas CustomLine switches (TOs)..If so, you can rub/sand away the black coating on the frogs..
I believe Atlas does this to preserve the pewter metal while hanging long periods on display racks in stores (maybe)..
That little protruding ring at bottom of frog is for a neutral wire to be screwed down to from a power-routing ground throw set up of some kind..
But it looks like you are going to have the longest diesels doing the switching anyway. So, such long wheel based locos are not likely to stall even if you do leave your frogs cold...
Here's a little scenic tip: Paint the 4 insulators surrounding the frogs and any other rail insulators with chrome enamel..or chrome nail polish..