Congrats on buying the car and getting out on-track. When you say fluids have been changed, did you get the radiator flushed? If not, I probably would. Just to ensure there isn't air in it and to help with what's already weak cooling.
I would also consider getting the transmission fluid changed as well, if that hasn't been done.
If your brake pads are not new, or close to new, I would watch them throughout your sessions. As the pads go below 50%, the heat generated and retained/transferred to the rotors gets worse.
If you don't have one, get a good tire pressure gauge. Run a few laps in your session, pit, and check pressures. As has been said, you want to get your tire pressure around 32ish PSI hot and it takes time to work that out. Pressures go up more than you think they would after a few laps and it's important to monitor them. And then remember to go slow on our outlaps to get pressures back up after they cool.
If the track is hard on tires, or a specific tire, keep an eye on that corner between sessions. I run a track that's hard on right fronts and without camber you can destroy the outside shoulder in a day.
Have a great time and enjoy the experience. It will no doubt lead to more!