1) The first two weekends in Sept are fine. I would avoid the park though as soon as Fright Fest begins. That is when the real crowds return.
2/3) 25mph but there now is rumor the ride might not even reopen until end of August if at all this season.
4) 15.00 unless you have a Season Pass to another SF park then it is free
5) Sundays in August are mild-moderate. It is the heat usually that keeps the park free of crowds in mid-late August.
6) I would do Superman due to capacity, then Toro, Kingda Ka (line generally is not bad if 4 trains run), Bizarro, Batman, Nitro, GASM, Dark Knight, RMT.
7) I doubt you will need a flash pass that time of year but if you did the regular pass is a good deal if you want to scatter around the rides. With the gold you basically just skip the line right away.
Again I doubt you will need it.
Enjoy the park. It has been a great season there so far. The park is clean and it seems to have a fantastic staff now.