When to put the amp in, ..now or lateR? Options

[amory_Tarr]

Alright, i just bought an alpine 9805 head unit to replace the stock GT tape/radio player. Anyways, i will be adding some form of a RF Punch Amp in in the near future and was just wondering if me and my dad were to put the head in, would it make a differance in finding a used amp to put in now, or is that something that would not be made easier or more difficult if i didnt put it in when i put in the head? Also, how much wattage should i be looking at? for xmas im getting a front component set that'll be powered by the Fosgate(im thinking either the 45.2, 55.2 or 75.2?) and then use the Alpine to power the rear two. Thoughts, suggestions?

Thanks,
Amory

[amory_Tarr]

One other question, for about $15 more i can get a 4 channel vs. 2 channel amp. But i'm running very low on cash and wouldnt be able to swap out the rear speakers. If you had to either power the 2 rear speakers (i have a 6 speaker system) with the 23rms watts from the alpine or from about 55rms watts from a 4 channel fosgate which would you choose? and would the fosgate overpower/blow out the rear speakers?

thanks again everyone,
Amory