Novas,
You are absolutely correct, the answers to all your questions are on here at least 10 times !!
The fact that the threads are 3 years old and still used reflects the fact that all the information on the preceding 40 odd pages is still very relevant. My (obvious) advice would be to read through as much of it as you can and then fire off any unanswerred questions you still have.
In answer to the ones you asked though :
1. No ; Yes
2. No ; Yes ; Not Really
3. Yes ; No ; Read through the threads, identify people from units you want to visit and ask nicely !
4. " A level commensurate with your previous experience but that shows you have put some background work in". I.e work on improving your knowledge from where it currently is but don't waste your time learning the thrust to weight ratio of a 747s engines (don't laugh I've seen people who have! ) Because I (and most of my collegues) don't know the answer and am therefore unlikely to ask the question at interview.
None of the above is intended to be facetious or put you off asking questions. In fact is shows that you are keen to learn which already gives you the jump on some of the people I interview ! I mean simply to point out that the answers are already out there if you're prepared to look hard enough.