Autopilot would require the N900 to be able to send servo control pulses (which would require USB host mode and some sort of USB->servo thingy [these can be built form microcontrollers easily but unless you have old PIC16Fs laying around you probably would want to go with more advanced uC and then you could go to full arduino and get all you need [except python...] without using the N900).

Make no mistake: I appreciate the geek factor of doing something like this with the N900 but it's not really an optimum (or even sensible) approach to solving the autopilot (or datalogger, or telemetry) -problem. But not everything is about the optimum or even sensible solutions, look at TCP/IP over avian carrier for example...