The Arduino can not directly drive a motor. For that, you need some kind of transistor to switch some external power supply that powers the motor. If you want speed control, and to be able to run the motors in both directions (helpful when the line backs up), then you need an H-bridge. Buying one pre-made is generally better than trying to build your own.The pressure sensor is, I presume, to determine how heavy the suitcase is, so you know how much help to supply. I'd think that something in the handle to sense when the suitcase is being pulled or pushed would be useful, too.
To make any useful contribution to something as heavy as a suitcase, you're going to need quite a bit of power. Packaging and installing all the components on an existing suitcase would take a substantial amount of work.An approach I've seen used successfully on electrically assisted bikes is to fit a powered trolley behind the bike to act as a pusher. It seems to me that you might be able to come up with a two-wheel trolley that one corner of the suitcase can sit in, containing a battery and motors operated by a pressure sensor on the suitcase handle. If you're feeling ambitious you could integrate this with the suitcase's own integral wheels, but I think that will be much harder to package and you might want to defer that. Perhaps you'll have time for that as well during your twelve weeks, but I suggest you get the standalone version working first - very little of the work on that will have been wasted if you decide to continue with 'phase 2' in the same project.In other words, take an iterative approach and do the parts that will show the greatest value first. That's the electrics and electronics and control logic.
To keep the project simple, you could get an inexpensive servo tester like below and a big inexpensive servo like the bottom ones (modified for continous rotation) to drive the wheels. Make a push/pull or squeeze setup for the suitecase handle to operate the servo tester pot as needed to control the servo foward/neutral/reverse rotation. http://www.hobbyking.com/hobbyking/store/__14774__HobbyKing_Servo_Tester.htmlhttp://www.hobbyking.com/hobbyking/store/__8296__Turnigy_Servo_Tester.htmlhttp://www.hobbyking.com/hobbyking/store/__291__189__Servos_and_parts-X_Large_Servo_50g_.html
Excuse me for my stupidity in the Arduino project field but does your method involve the use of a Arduino Uno board as the assignment requires that I use and Arduino board included in the project.