Can you have two amps in a car?

Most of the amplifiers include this functionality in internal wiring. If pass-through functionality is available you can connect two or more amps together. You can connect pass-through output on the first amp to the preamp input on second amp and up to so on.

How many speakers can you hook to a 2 channel amp?

You can easily connect 4 speakers to a 2 channel amplifier just by keeping in mind the impedance of speakers and dividing the power equally to both the channels.