Since visitors to the upper floor must go to the 124th floor first, then switch elevators, I noticed those with fast track tickets to the 124th floor were given priority and we had to wait a while until they all went up which I thought was a little strange. There are snacks in the waiting room along with a welcome drink on arrival to the 146th floor, but I’ll leave it up to you whether spending the extra cash is worth it.
The Burj Khalifa is located next to Dubai Mall and easily reached by Metro (with a fairly long enclosed walkway from the metro station to the actual mall). There are plenty of parking spaces at Dubai Mall if you have a rental car and we didn’t have too much difficulty getting in or out. I still prefer to take the metro but we had a visitor on crutches so driving seemed like the best way to go.