First and foremost, do NOT use that GPU, it's pure rubbish!
You can get Slices 1,2,3,4,6,&7 all on a single ethernet port of a 660. The loading capacity of that configuration is only 536,000 pixels and a single ethernet port can be loaded up to 655,000 pixels. So I would use port 1 (with port 2 as a redundant) for those slices and then use port 3 (with port 4 as the redundant) for slice 5.
A single 660 can do all of this from a single output of your GPU. No need for any other hardware in line.
I mix and match different pixel pitches, makes and models all the time on Novastar, there's no problems doing that at all.
You can find 660's for $300.
Here's a pixel map of how I would configure my 660 to look like when mapping this: