Let's clear up a tad of mis-information:
A - The assets are not available until once you're finished with the missions in which you take control of the mansion. When you finish the necessary mission, a very public display saying "All Assets Can Be Purchased" comes on.
B - The car dealer is a bit north of the airport, and, when fully complete, generates $9000 a day.
C - ALL ASSETS MAKE MONEY! The strip club, unfortunately, requires a stupid view of this stripper in a private room. It takes a bit over six minutes. Then missions are available.
D - YOU DO NOT have to do the road races for the car dealer to make money.
E - If the icon outside of an asset is red, you haven't yet finished 'Cop Land' and taken control of the Diaz mansion. Do so.