Thank you, all good information! It’s a low mileage 5.0 that I’m still building confidence in so in the stage of making it safe and reliable. New to track days so need seat time more than anything.What's on the car now, and when was the last time the brake fluid was changed? Also, are you new to track days or have you run them before in something else?
You want to use at least a good DOT 4 brake fluid, or a DOT 5.1, never DOT 5. If you don't know what's in the car now, or if it's older than a year, flush with new. If it's good and fresh, you can just do a bleed before each track day, and maybe after as well. Note that "flush" is different than "bleed" - bleeding is just removing any air bubbles at the caliper; flushing is replacing all the fluid in the entire system.
For pads, there are several brands that folks here like, each with different compounds. The compound determines the temperature window the brake pad is "happy" in. "Street" pads will work from cold but will disintegrate at temps that an experienced driver can create on track. "Race" pads like to be warm/hot to work and will hold up under extreme heat, but will squeal like a stuck pig and destroy brake rotors when cold.
There are some companies that sell "street/track" pads that will probably work for someone new to track days that is not using the brakes that hard. Once you get more confidence and use the brakes harder, you'll start needing a set of pads for the street and another set for the track. Some pad manufacturers (e.g., G-Loc) have street & race compounds that are compatible with each other, so you don't need to change the rotor. Other pads may need to have their own rotor that's been bedded-in with that compound.
Note that the traction control system on the Mustang likes to apply rear brake, and can end up overheating the rear pads, and/or melting axle seals from rotor heat. If you're still building confidence on track, at least set the traction control to sport mode (car on, press brake pedal, push TC button?). Ideally, you want to turn it off completely (car on, press brake pedal, hold TC button down for 10 seconds?).
If you look at the Supporting Vendors scroll near the bottom of each forum page, you'll notice Optimum Performance (aka OP Mustang) and KNS Brakes, as well as EBC and Cobalt brake pads. Please support them if you can. OPM and KNS are both very knowledgable on Mustangs and can help put together a package that fits your current needs and has some room to grow.
Some tracks are harder on brakes than others; @Bill Pemberton will have a better idea of track-specific brake needs in your area.
Other than brakes, the number one modification I'd recommend is camber plates (Vorshlag, Maximum Motosports, Steeda, Ground Control). They will keep you from grinding off the outside shoulder of your tires, or at least reduce it. And then tires that have decent grip but can take a full session without getting greasy. For novices, seat time is the most important thing, so you want a car that is durable enough to be driven hard for an entire session, for all the sessions in a track day, and doesn't change how it responds to the same driver inputs through a session. You'll learn fastest if your car is reliable and repeatable.
I always recommend making upgrades in this order -
Make it safe.
Make it stop.
Make it turn.
Make it fast.
And remember to have fun.