Very Noobish Question!
 

Ok, I already have a 12"sub in my car but want to upgrade my components and rear speakers.

If I wanted to run 2 amps (1 amp for my speakers, 1 for the subwoofer), would I need to get a stronger batter/alternator?

What do I need to make this work and be reliable? I do not want any interior lights dimming etc..

TIA

What car do you have?
What amps do you have?

Do your lights dim already with that single 12" in your car? If not then chances are adding an amp for your front and/or rear speakers will not change this. Of course ground upgrades don't hurt at all and can help your charging system out quite a bit.

I have an Integra and the lights do not dim at all right now and I want it to stay that way. I'll have to check on the amp model- it is some soundstream mono amp

When you say groud upgrades- are you referring to the ground cable wire?

Yes, ground from the battery. Its called the big three which is a wiring upgrade of your:

1) Battery to chassis
2) Battery to Engine
3) Alternator to battery

as an otion you can also upgrade:

4) Chassis to Engine
5) Battery to fuse box

Is it advisable to run a 5 channel amp to power all 4 speakers and the subwoofer or is 1 mono amp best and 1 amp to power the speakers?

I don't see many 5 channel amps floating around

Well, although 5-channel amps look good on paper, that mono channel is almost always pretty weak in most of the amps out there.

I prefer a good, solid two or four channel amp then run a mono class D amplfier for the sub(s). Class D's usually have tons of power and unlike class A/B amps, they don't use a retarded amount of battery-robbing power. They're pretty efficient.