That would be A 19mm or a 3/4" both the same.
As far as how to rotate, it's easier to just rotate same side front to rear, unless your roads have a high crown. (Like Iowa)
I can't help you on direction(I don't have a Si).
Don't use a torque wrench for removal's, just for tightening.
5000 is the rotation interval.
The issue with cross rotation is getting the car off the ground, and the safety of supporting it while in the air.
The factory Michelin's are not directional tires. The optional 18 Yokohama's are directional. Please use this link for proper rotation instructions:
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=43
When torquing down the wheels torque to 80 ft lbs.