You'll never really do an online 90 day report unless you did an in-country extension. Make your way to your local immigration office for an in-person report.
your phrasing isn't too clear. I believe if a dependant/spouse applies for an in country extension, it would be only be granted if the main holder also had an extension granted since an extension requires wholly updated resubmitted requirements. It's a little tricky to wrap your head around the logic process, possibly
When they ask how will you support yourself they want to know financially. Besides the 500K you would expect to show some passive income or savings etc.