The Pansonic Hpx300, HS400 and Aja Kipro combo has been working rock solid for us and I highly recommend it.
Have a look at the new Panasonic Hpx250 camera instead of the FS100, this will solve your hdmi issue(sdi out) and will match your other Hpx 300s a lot better.
The Kipro might be more expensive but is tried and tested and is a perfect match for the hs400 with its XLR audio inputs, Audio meters, up down conversion, and you can record all day on a 500 gb drive. Not to mention timecode in and out.
Better to spend the money now, on something you know that will work(because you have been renting it) than taking a risk on new technology and workarounds that one day might end up biting you in the ass.
Martin