Ideally, you would move from Solo to PDX using the same car. If it's street driven, you don't really need to do anything. Club trials is when the transition starts. Personal safety gear is first up. After that, it's up to you how much you want to start building your car up to match one of the Club Racing classes. At some point, it will become obvious that you need to stop driving it on the street, get a trailer and tow car, and you then have a dedicated track car.
When you move to Club Racing is entirely up to you. It would be a good idea to volunteer to work a Club Racing event or two or three to familiarize yourself with how events are conducted before going for your Novice Permit. The other big jump occurs when you do go Club Racing. It can be done without crew, but starting out, you really need someone to help you. The fatigue factor alone makes it challenging to drive and keep the car running.
Before you get to the point of a Novice Permit, you should contact your local Division Driver Licensing Chairman to find out how the program works in your area. When you make the move the most important advice you won't ever hear anyone tell you: Park your ego off the track property.