1) You should be able to get everything to work.
There are a couple of different ways to mount the laser, we have some pictures of how we do it here. http://www.iheartrobotics.com/2012/03/in-stock-even-more-turtlebot.html
The TurtleBot Power Splitter can be used to provide power to separate devices. However the Create is only capable of supplying 1.5 Amps of current. If you attempt to pull more current, a protection circuit will reset the robot. Also the charging system is limited so if you try charging the robot without shutting down the Kinect, Laser or Arm the battery empty faster than it can refill and may damage the battery.
2) Maybe. I think it can be done, but as far as I know there is currently no way to charge the battery without the robot. Also, the laptop battery often seems to be the limiting factor.
3) The strength of the arm somewhat depends on how you are lifting.
We have not tested this fully, but the best measure is the servo motors maximum specifications. The Robotis AX-12A servos have a Stall Torque : 1.52N.m (at 12.0V, 1.5A)
The arm itself weighs about 0.4kg and is about 30cm long. The first servo can hold 5N in position and assuming all of the weight of the arm is at the end, the mass of the arm applies a force of about 3.8N which means the arm should be able to lift about one apple. Keep in mind this is a rough estimate and we have not tested it.
4) Someone from turtlebot.eu may be able to correct me, but they are similar in overall performance. I believe the the Roomba 521 may have slightly better wheel encoders but it lacks a gyro. Also, I think there is more room on the Create.
