Well you just removed the primary cats on the car, so some smoke is to be expected. It could be condensation or packing/manufacturing substance burning off of the exhaust, but IMO it's more likely that your car is blowing by a small amount of oil that is then being burnt up. Happens to alot of people when they go catless, you just didn't notice it with the primary cats in place. It's far more likely that you're burning some oil (common on N54s) than burning coolant (not so common), if it's oil the smell will truly smell like combusting motor oil and gasoline. Coolant has a distinct sweet smell to it, burning oil just smells like combustion with a bit of melting plastic to my nose at least. Nothing to freak out about most likely.
E88 N54 Alpinweiss/Coral Red/Motiv HTA 3586r Tial .82AR/Other stuff...652WHP
F30 N55 XDrive EBII