Hi,
In desiging amplifiers, you have to have experience to make the right selections. In your case, I would make the following remarks:
1.With this bandwidth, if you really want a flat response, you need feedback! You can try by selecting a really fast opamp. Or RF transistors will do well also. But you will have to take care not to use too many stages before applying feedback, because instabilities could occur! Another option is to use mismatch to flatten the gain of the amplifier. So the operating frequency defines the transistor or amplifier to use!
2.The output load defines the bias current of the last stage. When applying feedback you can use a power amplifier for the last stage (like in opamps). If not you need a class A stage to minimize output distortion. The maximum output voltage swing is the output current swing times the load resistor!
3.The stages before the output stage can have smaller bias current because the signal is smaller there (linearity).
4.You need 50 voltage gain, or 34dB, you need at least two stage to realize this. If you use feedback, perhaps three stages are necessary. But beware of oscillations! Often it's better to use two cascaded stages with feedback of their own then!
5.It's not common to define Ai in discrete amplifyers (different from current amplifiers in IC design!). Most of the time, we only specify voltage gain or power gain. Ai puts a restriction on the input impedance of the amplifier, as it should be Zout*Ai/Av, or about 50Ohm.
These are specific remarks for this case. The selection of the optimum topology depends on other things, like best gain, linearity, noise performance, .... Read some literature to find out about these!