Do you already have the 7x10s + splits, or are you still looking to purchase?
** Warning: the following text represents my opinion only ***
If you intend to run a subwoofer, I would recommend 6" 2way splits in the front (from memory the stock skyline front speakers are 6") and 6" 2 or 3 way components in the rear parcel shelf.
Depending on the quality of your headunit, if you were running only one subwoofer you should be able to run the four 6" speakers directly from your headunit using one amplifier to power the subwoofer.
As far as 'how you do it': the easiest way to hook it all up is to make sure that your headunit has enough RCA outputs for each of your amplifiers, you then do not have to worry with cable splitters which will only decrease the quality of sound further.
I'll cut this post short here as to not get too annoying... PM or just keep posting here if you've got any more questions, or any specific questions about what I've just rambled... or whatever... uhoh.. i'm still rambling....