I DIY a splitboard about 8 years ago and used it a couple of times. I can't help you with the bindings, but there is one mistake I made. I used a full rocker powder board. Rocker was all the rage at the time and hey, if your split boarding your riding powder right? Well, the rockered board made skinning difficult. You have a much smaller skin contact patch and the board flexes up with each step. I would recommend using a stiffer board with traditional camber. That way each plank will perform more like an individual ski with each step/slide while skinning. Good luck with your build!
This is really valuable feedback. I was thinking as you had about the pow board idea. Definitely will reconsider what's in the "splittable" deck stack. Thanks!