ChanCafun: that’s awesome, it looks really good. I assume you didn’t have any trouble figuring out the layout and spacing of the two 2×10 headers. I put them on a standard 0.1″ grid so it would be easy for people to produce their own accessory boards.
What SDI-12 sensors are you using? I don’t recognize those 6-pin connectors, but they look like they might be useful for times when the 4-pin Grove socket isn’t big enough.