push pull power amp

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