An Optimate was a supporter of the Senatorial class who were benefiting from the massive wealth flowing into Rome after conquering the Mediterranean area. This created a huge problem after 100 of thousands of slaves were brought back to Italy and eliminated the small Roman farmers. The populares took advantage of this, but it ended up in civil strife and war for about 80 years.

The Optimates were members of the ruling class of ancient Rome. They were the aristocracy - old blue-blood families with seats in the Senate. The history gets a little muddy since there were politicians from that class who embraced populism, but Sulla wasn't one of them.

Yes.

A good overview from A.H.M. Jones, Augustus, from the first chapter, "The Breakdown of the Republic":

https://plus.google.com/104092656004159577193/posts/U7mLJYGy...

(The book is brief but the remainder is about as similarly dense as this overview -- if you're not already familiar with Roman history and particulars, there's not quite enough context to grab hold of. There are better, longer biographies which should be easier reading.)

Yes. But politically, he's running as a populare. This happened in Rome as well - senators would take a populare position on a particular issue, even though they were optimates.