You can add the grills at the VPC.
For the Sirius...that I'm not sure of. You should be able to get that option directly from the factory.
Frankly the Grills take 5 minutes to put on, may be worth just doing them yourself. I had my dealer put them on at the VPC for $170 only because I didn't want my wife wondering why I was disassembling my car on the first day I got it.
Honestly it doesn't matter where they do the work, just make sure they don't try to charge you $300 for snapping on 2 plastic grills. The Sirius should just be able to come with your order, or are you trying to add it after your car already was built?
Current: '15 M235i Vert
Previous: '13 335i, '08 TL-S, '00 Corvette