I probably wouldnt worry too much with the filters. If you use them or want to, I would apply them about as usual, at least on the gun tube, roof, upper hull, side skirting, etc.
With washes, I generally apply a wash over the whole model, making it darker around details, corners, etc. But over zimmerit an overall wash gets between the zimmerit ridges and makes the model dark or muddy looking. So I wouldnt do an overall wash... just a spot wash around details.