In post egtrra time, the real question is why are you doing this? It seems to me one PS plan would suffice if you just determine different rates for different groups (new comp approach.)
It seems you are setting yourself for a lot of headaches from the get go (approval from the IRS for starter,) then wait until you have to file three 5500, one for the PS, one for the MPP and probably one for the Master Trust you will end with if you comingle the assets from the PS and the MPP into one trust.
On the other hand, the benefit of having an MPP is ...
wait a minute, there isn't any.