Do the xbee XTend 1 Watt modules work for telemity in place of the 900 pro's?
What telemetry gear is the apm2 hardware (purple board) going to use?
Is an RC receiver / transmitter required or could all control be sent over xbee modules?
When telemetry link is lost does mission planner continue its course?
If telemety link is lost and the aircraft comes back into range will the link reestablish?
How many feet line-of-site should 2 xbee 900 pro's get?
On this forum, why does the chat window come up as a blank white square in every browser I have?
Any radio modem that uses regular uart serial communication at a standard baud rate between 9600 and 115200 can be used. Beyond that there is no specific requirement other than the radio modems provide a transparent link.
An RC tx/rx is not required, but makes getting things set up properly easier.
Mission Planner has nothing to do with what APM does when telemetry is lost. There are a variety of failsafe options that can be used.
LOS Xbee range is highly dependent on what antennas you are using, how much rf noise is in your local environment, etc. For Xbee Pro 900 (non XSC) modules with "rubber ducky" dipole antennas you could consider 3000 meters an upper limit in most locales.
I dont think that completely correct. For example the xbee xsc's are limited to 9600 baud, and can not keep up with the minimum data output to the ardupilot mega.