Electronics upgrade to eS95

I will be installing a eS95 at he helm of a sailboat. I currently have three ST60+ instruments D/S/W up next to the wheel. I have a Raystar120 on the stern and a TRIDATA down in the cabin. What is the maximum number of Seatalk devices that can be connected to the Seatalk to Seatalkng converter. Can I select which GPS data source to use in the system? The boat also has an old Pathfinder Radar that I would also like to connect to the seatalk buss to provide GPS data to the radar.

Thanks
george