You should do a little bit of research first by searching this forum. But to answer the easy questions, the coupe basically has a different back of the car inside and out compared to the hatch back. No 240SX was ever AWD or 4WD, they have always been Rear wheel drive which makes them excellent drifting cars.
As for the engines, they each have strengths and weaknesses depending on what your final plans are for them. If you dont plan on modding the engine to make a 3-350 + hp then get an S14 or S15 engine, but if you want to put up really big numbers with less hassle then the S13 engine is better. Its also cheaper.
BTW this is a hatchback or fastback.