You do not need to purchase a Super Nintendo World area timed entry ticket in advance, as the park is generally open to all visitors. You just need to manage your entry time wisely and avoid peak hours to enter the area smoothly.
The Kansai Have Fun Pass Premium is a better option compared to the regular pass. The standard Kansai Have Fun Pass is limited to only 3 attractions, which may not be enough if you want to experience more rides.
For major attractions, reservations must be made at least 2 days before the entrance date, so make sure to plan ahead.
Overall, a great experience at USJ, just plan your timing and passes carefully to maximize enjoyment.