Hey Dave, I won't be able to help with all questions but il offer my advice :)
the service interval is long life so every 20k miles or 2 years I believe.
I would deffo ask Audi about the kick plate as you should get a 10 year anti perforation warranty with the body. Don't know how this will apply but I imagine it should be covered.
With regard to mudflaps I'm unsure but I don't see why you can't get front ones.
Mum unsure on the wheel offset, sorry.
Hope iv helped :)
cheers
steve