Hi Omar,
July will be very hot, so shorts will definitely be enough. You will in addition want to go into the water very often, as sometimes it gets toooo hot on the beach :)
regarding kite-sizes it is better you take all you have. you can have very low wind days with 10-12 knots as well as really strong winds. To el gouna i always take all kite sizes i have: 7,9,12… and sometimes a bigger kite would have been good too.
it is not a spot where you can say it will never be over 17kn or something like that. be prepared for all from nothing to lot :)
cheers
Mathias