Amplifier MOSFET (25m - 5V)
Providing a voltage gain of 200 on to an 8-ohm load, linearly, with a single stage amplifier and without feedback would be rather hard. The only way I can see of approaching it is by using a transformer to match the impedance of the load.

You can start with a two stage amplifier, common-source into source-follower. That way the output impedance of your voltage amplification stage can be paired with a low-impedance output stage to match the impedance of your speaker.