how many parts would be interchangeable from a 4th gen and a 5th gen

Not very many. There are probably common items scattered around in the bits-and-pieces department, and some underhood / driveline commonality, especially between late 4th and early 5th. But by and large, they are very different platforms.

Engine and Transmission, Door Handles and window cranks, Light bulbs, some fuses, tires and possibly Rims.

Different trucks. With work some other parts can be used but you're talking about a Metric vs. SAE in a lot of situations. Different sized frames glass, doors, fenders, front clips you name it.

alright thanks, does anyone know a good place to get parts for a 4th gen elky or am i pretty much just gonna have to look at salvage yards?