FvM - I said my comments were "general" in the absence of frequency and board information. We don't know what materials he's using, modulation method, frequency, etc, etc.
With regard to the stackup, there are no dummy layers needed. Simply put the two reference planes inside as the core, the two outter layers become copper on prepreg . It is likely he will need/want a power plane in addition to a "ground" plane. Either plane will make a satisfactory reference for RF circuitry on the top and bottom layers. I've designed many commercial RF devices in that manner over the past forty years.