Nice!! Congrats man, loads of fun.
It was the OP's first track day.
I used to club race motorcycles and have done numerous track days on bikes, but never in a car. There's a universal saying when it comes to track days, and I think it applies with cars too:
A good track day is when
...you come home in one piece
A GREAT track day is when
...you AND your (car/bike) come home in one piece
Sounds like the OP had a GREAT track day(s)!
All the technical stuff and lap times and what not, it's just gravy, and comes with time and experience. Hats off to tracking your M5! At Barber, no less - what a beautiful facility.
I look forward to posting a similar experience sometime in the future with my X6M