push pull power amplifier design

hello,
I would like to design a linear push pull class-AB 20W power amplifier in the HF band using similar RD16HHF Mitsubishi transistors. Here are the questions:
1- In this scenario, how much gain can I get from this push pull amplifier?
2- How I should calculate optimal values of the feedback network, to achieve maximum flatness over the entire bandwidth?
3- How can I estimate the input impedance of the power amp?
4- How much excess power (than required) is needed at the output of the previous stage to maintain the linearity of the power amp.?
5- What's the reasonable values of the 2nd and 3rd harmonics (relative to the first harmonic)? In what percentage of the output power I should measure them?

any help or hint about the above mentioned problems would be appreciated,
regards
bye

All those questions are related to design problem.It's you who will decide design constraints,definitions,topology etc.
There won't be any sense since if you don't have any design skills or you have never designed such circuits because you're asking fundamental questions of design.