Is it possible to have the GPS connected to I2C instead of serial so then we only need 4 pins for the external compass and GPS module?
In theory yes, in practice its unlikely anyone is interested to put up the software development effort just to save two wires. You can use the CAN GPS from Zubax: https://zubax.com/product/zubax-gnss-2
Is the Pixhawk 2 designs on this project allowed to be used to manufacture the Pixhawk 2?
Is the Pixhawk 2 design the same as the one used by 3DR in the Solo?
Does the normal firmware in Mission Planner work on the Pixhawk 2?
Sorry for all the questions just trying to work out how I can get into the development on an updated version of the Pixhawk system. We have been using them in our vehicles for several years. We have been approached by several organisations to develop new vehicles which I would love to update the Pixhawk for as well.
Yes, but FMUv3 has already been superseded by FMUv4. A full version of that design revision should become available shortly.