Oh yes, it’s crazy busy. But it’s rare for USF & IOA to close because of capacity. But knowing that last Christmas covid was still prevalent, it could happen this holiday season with the continued revenge travel. You would be safe from this if you stay on site.
You could very well need close to 4 days if you don’t have Express Pass that skips the standby line at most attractions. The 3 premier hotels include this perk though. 2 nights staying here would get you 3 park days with EP. You would only need to do standby for Hagrid’s and Velocicoaster.