You don't start a critical or sensitive design by deciding how many layers it will have.
You start by deciding the best layout for both components and traces that will give the results you want. Crosstalk, resonance, shielding, impedance control, power, frequency, etc. - all determine how wide and thick the traces will be, what material the dielectric should be, how many and where the reference planes will be, how many signal layers you might need to get the desired isolation and signal continuity, etc.
Once you have the component and trace layout determined to give the desired result, you begin to get a feel for how many layers it will take to achieve your goal. Stackup is always done in pairs of signal layers, and pairs of planes. Odd number of either will usually result in built-in stresses resulting in cupping and/or warping of the board. The stresses only get worse by soldering heat and component weight.
Follow Tanuki's advice above - get the study material and learn about the science of PCB design. In addition to the book recommended by Tanuki, I would also recommend "High Speed Signal Propagation: Advanced Black Magic" by Howard W. Johnson - it is aimed at high speed digital boards, but applies to RF work as well.
Of course, you can always do the job cheaper, with fewer layers than I might use, but the end result will be less than your best.