As above you can use every week if you like it will not remove any clearcoat but i normally detail my car every 6 months but have done 3 times a year when i was showing my last car.
AG EGP is worth poping on over the top of SRP gives protection and a nice base to top up with a wax.
With the Z4 i normally
Clay
AG SRP
AG EGP
Victoria Concours x 3
Have you thought about using a QD after washing once you have the car polished and waxed keeps that nice glossy look this one is very good
http://www.seriousperformance.co.uk/Products,78,toView_337.html