1. It all depends on the situation.
2. It all depends on the situation.
3. It all depends on the situation.
4. It all depends on the situation.
5. It all depends on the situation.
No seriously, #1 really does depend on the situation that you are in, and how closely you are allied with france/russia.
For #2, just send out messages to all of your neighbors, and open based on the responses you get from them. If you are looking for a list of openings (and this goes for your question about italy too), you can find them here:
http://www.diplom.org/Online/Openings/
3+4. That's a matter of personal opinion. In my experience, an all out attack against italy can work, but only if you pit Russia and turkey against each other so they don't make gains on austria too quickly while he is fighting you. If not, bide your time and once the time is right, go for the stab (this could be as early as autumn 1901 or when you are turn away from the solo.)
5. Austria's survival depends on the decisions of those around him. If italy tries to attack you, you're pretty much done. Thus, Austria is the country where its most vital to diplomacy with others to make sure that they ally with you. if you can get into an alliance with one of your neighbors and get a 2nd to ignore you or join in on the alliance, you should be set for early game. After you get past 6 centers, you are tough to stop due to your close proximity to so many centers.
I hope this answers all of your questions.