I am upgrading the components for the first time on my Giant Defy Advanced 4 2011. 

I am 6 foot 5" tall and 220 lbs. and I ride 25 to 45 miles every time on mostly flat terrain in South Florida with occasional rides over the 1 mile bridge with high elevation increase.  I want maximum speed with the mix of new components and my budget and taste calls for the Shimano Ultegra 6700 Group Set.

I found a great deal online, however, I am being asked a few questions I don't understand when trying to choose the components I'm ordering. 

1.  Cassette type:  11/23 OR 11/25 OR 11/28 OR 12/23 OR 12/25 (Which one should I get and what does this mean?)

2.  Front Derailleur:  Braze on OR 32mm Clamp or 35mm Clamp (Which one and what is the difference?)

3.  Bottom Bracket Cups:  English Thread OR Italian Thread (Which one and what does this mean?)

4.  Crank Set:  175mm 39/53 is what I was told to upgrade to...not sure that affects the above one way or another?

Thank you for the assistance in advance!!!!