Im pretty sure this is all mentioned above but if not:
1. incentives are from BMWFS so you will need to go through them lease or finance to qualify
2. you can lock in rates with your dealer (run a credit app) which will lock you in for 60 days for a east coast dealer and 90 days for a west coast dealer
3. when you are locked in you are able to pick the best months rates in the locked in timeframe as long as you take delivery of the car in that locked time. Once the lock runs out you will need to re lock again (run credit)
you can lock in on BMW website or at your dealer. just make sure if you lock in online you select the dealer you want to lock in with and also confirm with them they got it.
Always lock in pricing etc.. before you order. Don't kinda of agree get it in writing otherwise you will be behind the 8 ball once the car comes in. Also take a look at the whole deal when negotiating not just the amount of MSRP as APR and MF can be marked up and also various random fees
happy hunting