-The tutorial didn't show how the XBee modules are configured. I know they are preconfigured to work on point-to-multipoint but demonstration would still be helpful.
The XBee's in SquidBee are in transparent mode, that's the easiest way to communicate the SquidBee's. The only parameter changed is baudrate, (set to 19200 bps BD4). Anyway with X-CTU it's very easy to change the XBee parameters.
-The tutorial only showed 2 Squidbees communicating. How about if there are two motes sending data to gateway. How will that be displayed to the serial monitor?
If there are more SquidBee's, you'll see all the data in the monitor, as all SquidBee's are similar programmed, you should change the program, using a different id to any SquidBee.
-It would be nice if the tutorial show how one mote will be configured differently from the other motes. I know that network layer configuration (XBee) and application layer configuration (Arduino) will be different with all the motes but it is nicer if we understand the details.
It's very easy, using Arduino IDE and the code in the tutorial, you can change that program as you need.