hardware reverse engineering

I have basic knowledge in electronic, programming, and some experience with Arduino and I want to join it together and start reverse engineering of hardware devices. I want to learn how devices, microprocessors communicate (eg. learn their protocols), be able to disassembly microprocessors.

My questions:

1. AFAIK I need logic analyser, should I build one using microprocessor (or Arduino) or buy some inexpensive one?
2. What other tools do I need?
3. What books, pages should I study?
4. What are the biggest pitfall here?
5. Is such RE legal in United Europe?
6. Any easy points to start?

Arduino) or buy some inexpensive