I wouldn't leave to front components powered by the deck. In real life you are gonna see around 20-25 watts per channel out of the deck(always look to RMS not peak power). Seeing that I would go with the 4-channel (unless you get a seperate amp for the insides) only problem here is that you say you have 3 6X9's and you are adding 2 more sets of wires to the mix with the fronts's meaning you would need 5 channels. The solution I would go with in this case would be to power one of the 6 x 9's off the deck this way you don't HAVE to buy another amp. The only other solution would be to double up your channels on the amp running 2 speakers off 1 channel, I personally would not do that. As far as amps go I would suggest you stick with sony(since you seen to like them alot) maybe try the XM1600GXD, or XM2150GSX. If you are going to buy all those at once I will hook you up with a real good price, if not I can still beat all all the prices you seem to have so far. Here is my pricing:
Sony XSHF600G $250 shipped
Sony CDX-M730 $309 shipped
Sony XSL1046 $110 shipped(I can't beat their price on that they must have gotten a special purchase) If you get it all at the same time save on shipping and save some more $. On the sony amps I can do $180 shipped for the 2150gsx and $270 shipped on the 1600gxd. E-mail me if you have any other questions!