[TransamGTA350]

I'm in the camp of just take the car as is and go do some autocross events and Novice track days. Just upgrade your brake fluid and go. Don't worry about tires (yet), for the first few events. Once you start getting quicker, then a 2nd set of track wheels/tires makes sense. Leave the car alone as far as other modifications for now. Get seat time and work on your skills and extract as much as you can out of the car the way it is. After a while, you'll start to know what the car isn't doing for you and what you want it to do and then decide what to change. Or, you may decide that it's not worth modding this car and you move on to a different car, treating this car more as a learning tool. Nothing wrong with that. Often people start making changes to their cars way too early when really they just need more seat time.

You mentioned SCDA. I ran with them as a novice and enjoyed the experience. Their instruction and focus on safety was very good.

If you want to get into more competitive events, whether that is SCCA Autocross, Time Trials, etc., you need to look into the classes you would like to run in and evaluate how competitive your car will be and/or what it will take to get there. But, in order to be competitive, you need seat time and local autocrosses and HPDE events are a blast to do while you're learning.

The path forward will become clearer as you move along it.