Re: Fusion with enginer kit
there are lots of threads at priuschat.com. I have not seen Enginer discussion on anything but Prius II/III myself.
It sounds like you get to know the guy at Enginer well through the process of returning failed cells and such. You need to be comfortable tinkering with batteries to keep them balanced.
But I would recommend the priuschat threads highly. They take you through self-intall, troubleshooting, etc.