Thank you for posting your videos! They will help inspire other people to get their Mustangs out on an autocross course. It's great to see the car finished and out there attacking the cones. You did a really nice job of chopping time off over the course of the day! You seemed very comfortable out there, and it never looked like you were at risk of getting lost on course.
It's always tough to give advice on a course I didn't actually drive on myself, but I noticed a few things in the videos that might help you find more speed out on course:
1. You can be 1 or 2 degrees more aggressive on the throttle just about everywhere. There was a lot of open space on that course. It looked like you were attacking cone-to-cone in some places, instead of looking ahead at long stretches that were "fast-into-fast" elements. You also could have stayed on the gas through multiple widely-spaced elements (especially leading into the finish). In addition to being more aggressive on the throttle, increasing your duration of acceleration (getting on the gas a little earlier, and staying on the gas longer) will shave a lot of time off your runs.
2. You can move your inputs closer together. It sounded like there was a lot of time between when you let off the gas and when you got on the brakes. Ideally, you want those inputs to be right next to one another (use the gas until you HAVE TO use the brakes). Generally, any time you're coasting, you're losing time.
3. At times your line was really tight (which is very good), but at other points, you were too far off of the cones (which isn't ideal). You can find a lot of time in sweepers and slaloms by being tighter to the cones.
At your next event, take some time on your course walks to identify sections of the course, not just elements. Determine if they are "fast-into-fast" or "slow-into-fast", etc. That will help you string elements together. Once you've identified the fast sections, find the hidden straightaways in those sections, and go a little faster for a little longer (increasing by safe degrees on each run). And, if there are long sweepers, try to find a point in the middle of the corner (or sooner, if possible) to start rolling on the throttle (your aggression exiting the sweeper will depend on the elements after the sweeper). Think of sweepers like a highway on-ramp: if there's no traffic on the highway (an open element after the sweeper) you can exit faster; if there is traffic on the highway (a tight element after the sweeper), you'll have to brake or lift a little to get through it.
You did a great job of keeping the car composed on most of the runs. That will get more difficult to do as you push the car harder. But, you've got good instincts for not driving yourself into trouble (overdriving/overlapping inputs).
It was really cool to see another awesome Mustang out on an autocross course. If you have any questions leading into your next event, please ask. I'm always happy to help.