Perhaps I can clarify for you.
You can fit any normal tyre on a run flat rim. The rim just has an extra lip to stop a runflat tyre coming off if deflated
You can run any correct sized rim on a Z4 so you can go with a package. Whole separate science on sizes and offset, but stick to stock for simplicity
Your choice of tyres but avoid budget that often come with packages
For puncture repair you can go for a BMW mobility kit off ebay which combines air pump and goo (my choice), separate airpump and aerosol or even aerosols that combine both.
This is what I use but paid just £30 http://www.ebay.co.uk/itm/GENUINE-BMW-M-MOBILITY-SYSTEM-TYRE-INFLATOR-71102229700-/252513997658?hash=item3acb01d35a:g:4aMAAOSw-itXwD0u