[Accord Man]

both are possible..

there are couple of good 5 channel amps on the market.. (kicker)..


but depending on your budget, a 2 amp setup will probably cost you less.. Considering you need a sturdier amp for the sub and not so sturdy will do for the cabin speakers.

No need to touch the alternator.
Your amp will have to push roughly 600w rms.. so the requiered amperage should be relatively low..