Few questions about teensy 2 + XBee configurations.

1) Do you have to run the teensy2 at 3.3 volts to use the XBee adaptor?
2) Is the XBee adaptor compatible with all of the modern XBee modules? I'm new to XBee, but it seems as if there have been quite a few revisions over the years.
I'm considering these modules:

3) Are you required to separate the XBee or its adaptor from the teensy while programming the teensy? I need this thing to fit in a very very small space, and as such I don't think I'll have room for all the headers etc, so i'm hoping to be able to directly solder these components together.

4) Are the XBee adaptors in stock? The stock count is 2 years old.