New to PAX but not Rocket League. Would like to try out the tournament when I'm there
Since it's played on PC, I'm assuming controllers are allowed for optimal play.
Are controllers provided or should I bring my controller and usb cable?
If I am attending solo, can I still sign up or do I need a team?
You do not need to sign up as a team AFAIK but if you sign up solo for a team event you may just be left waiting for a teammate. If you are really interested in this, it's best if you head to the PC area first thing when the doors open to put your name down.
You can also ask the event organizers that will be present nearby if you have concerns about finding a teammate. Everyone here has always been very accommodating and will surely help you out.
Xbox One controllers are plug and play with PCs with the detachable USB cable. I use a normal Xbox One controller to play on PC.