To power multiple Pis from one plug socket I use a 120w 10 port USB charger
as it puts out 5v / 2.4A on all 10 ports.
I went for this as I did not fancy hacking a psu and additionally it is silent. A couple of my ports power RPis fitted with WD PiDrives and there have been no power issues.
I use a USB powered gigabit mini switch but the most I have seen is a 5 port version.
I suppose you could use 2 of the mini switches which will give you 7 usable network ports (lose 2 ports to link the switches and 1 port to link to your network).
So 2 x switchs, 6 x pis, 2 x drives uses up all 10 usb charging ports.
Of course now you'd need to work out how to get all that hot air out of the case!!!