Michael Cole announced on SmackDown this past week that WWE achieved their highest first day ticket sales in the history of the company. He did not disclose the exact number of tickets sold.
The current stadium set-up is what is typical for WrestleMania, everything behind the stage is unavailable. It is unknown if and when WWE plans to release more seats.
The two-day combo tickets have sold out for the event and as of this writing none remain on Ticketmaster. As far as the individual nights go, only platinum seats or single seats remain for the event. Platinum tickets are priced according to the demand. 500 level tickets that normally go for $50 are currently listed at over $350 due to the demand for the event.
There are plenty of floor seats remaining for the individual nights for over $2k each. Sunday night has outsold Saturday night as of this writing. Tickets can be purchased here.