Q: Is new profile required? 
A: Yes.

Q: Career Status (F4) shows I still need to complete X amount of races in stage A but sponsor contract says complete Y amount of races. Which one is true? 
A: Rachel will alert you through SMS once you have completed certain amount of open world races, Career Status Bar seems to be hardcoded. You can also check the amount needed inside garage through sponsor contract menu.

Q: Is this compatible with X, Y or Z? 
A: Mods that don't touch URL races should be compatible. A slight heads up for addon car mods, you might need to tweak the GCarUnlocks yourself since some repetitive URL events are merged into a single event. 

Q: Some upgrades seem to decrease handling according to handling slider, is this a bug?
A: There is an artificial slider logic that gets affected by many factors, like turbo or NOS increasing handling stat for no reason sometimes. So yes it's a bug but it won't actually decrease the car's handling.