1.) Anywhere from 1 figure to about 10 figures per player. With some simple adjustments you can go higher, but it was designed with just a handful in mind.
2.) Nothing specifically pirate in the main rulebook. The Pirate supplement Under the Black Flag comes out in June.
3.) The standard size, 2' x 2' board with three models per player goes in about 90 minutes if you know the rules and your scenario is not overly complex. The demo games for new players take about 2 hours to get through.
4.) Not in the main rulebook. It will be coming though. The one for .45 Adventure is in development and will be out next month so Gloire will follow that.
5.) Rules for mounted models are in the book as are coaches. Boats will be included in Under the Black Flag, but ships and the like will not be done in great detail since the game is not about ship on ship action.
Hope that helps and if you have any additional questions, just post away.