Ok, one at the time:
1. Yes, you can and you must (you have to provide real personal information when you register a domain)
2. Yes. If it's expired, it's up for grabs
3. What do you mean? if you mean prolong the registration time, then yes you can. But you can't for example switch from "something.com" to "somethingelse.com". You have register the other domain sepparately.
4. Yes you can
Hope this helps.