UmCha

Hello I am new to this, so please bear with me! :) My A3 of seven years sadly needs a replacement engine to be useable. I have been told there is a problem with the pistons? Unfortunately I can't afford this, so am breaking the car for parts. Does anybody have any advice as to where to start? I paid a lot of money for a replacement gearbox three years ago, so know if I can work out how to get it off there is some money there. The rest of the car is in great condition, apart from a small crack on the front bumper. Where is the best place to advertise these parts, and is there an order I should be doing things in? Any help or advice would be so much appreciated! Many Thanks