Im a little hesitant here saying this.. but take tackle one thing at a time. I know cars are quite overwhelming, but you cant be afraid to work on the car. You will learn so much during the process. Sure youll make mistakes, but all of us have made mistakes.
You can boost a N42 with no issues. You will read dozens of threads about "which is better?". Well... depends on your goals. If you are pushing the ragged edge of the L28.. yes cylinder head and blocks make a small difference. But for your goals, you have little to worry about.
Trust in yourself, do one thing at a time, do your research and enjoy the journey my friend. Its much easier to first learn how to work on the car and do "add ons" to the L28 rather then swapping in a whole new engine and new wiring harness. Trust me its a pain. I couldnt imagine doing it as a first timer.