Id also suggest APRS for data transmission or something similar, APRS has a few problems, apart from being amateur band, its slow and would clutter easily with many planes in the transmission range especially when repeating packets. WiMAX might be good, but I understand it cannot be setup in an adhoc network like wifi.
I wouldnt bother with replicating things that already exist, especially existing instrumentation. As Im sure it exisits on just about every production plane and second hand plane around. I also assume that stuff would need to be certified if you want the plane registered and that wouldnt be cheap
Get the absolute basics working first, internet access and all things related to that are fairly simply. Forget about all the features, focus first on getting the low transmission layers working first ie mesh type network similar to APRS working first as it will be the most difficult part, which is pretty much not possible due to restrictions. About the only thing you can do is put forward a case to get some bandwidth that can be legally used for this project, or convince everyone to get a HAM licence.
Once you have the stable way to reliably broadcast and retransmit packet data similar to APRS, then work on the next layer like the actual data packet content, format and the management of them. Then you can use, display, manipulate this data