1) MOT is a test all UK cars over 3 years old have to pass. It's to show that the vehicle is roadworthy in accordance with the government guidelines. Details here: http://www.direct.gov.uk/en/Motoring/OwningAVehicle/Mot/index.htm
2) Make sure you get a receipt for any deposit, and ask on here for a local member or trader to view the car and make sure it's all up to spec.
3) See above, plus click on the following link: What to check when buying a Supra
4) As above, members help other members on here all the time in situations like yours. I'm sure someone will be able to help.