I want to switch out every part of my engine with a new one because it's old, it's a 2002 Audi A6 Quattro 3.0 liter...

just switch the engine??

here again.
If you're really set on doing this, I suggest buying a junker engine on the cheap that has no cracks or holes but something like knackered bearings or so. Then you can take your time and rebuild that to perfection. When you're done you can just 1 for 1 swap it into your car. This way you get minimal downtime and stress.

Do make sure it's the exact same engine code though. Those VAG cars have a lot of very very similar but not quite identical engines and you never know if one that has the same specs but a different engine code will be an exact replacement for yours.