Here's my season ticket history with my main team:
III: 1311 / 1429 / 1482
II: 1952 / 2259 / 2389
EBBL: 3209 / 3646 / 3825 / 3909 / 3954
Most seasons my team has either achieved a similar number of wins or improved a bit, so season tickets have gradually increased over time. Obviously promoting to a higher series has a big impact. A few of the top teams in the EBBL have 4,000-4,100 season tickets, so that's possibly close to the maximum.
With my Utopia team, my season tickets got to about 1,000 in IV but was only gaining about 30 per season at that point. Promoting increased it by 328, demoting after a 0-22 tanking season lost 277.
I don't have any details on the impact on attendance. My guess would be higher season tickets = more attendance (obviously), maybe more stable attendance regardless of results, maybe more impact on the expensive seats. Maybe the TV station affects it?
As EWB says it's mostly ignored as an area of study, because as a manager there's little you can do to improve it. Winning games / promoting obviously, but then we're trying to do that anyway :)
Thanks a lot. There is little data (very valuable for me) and it does not answer most of the questions, but it is an interesting starting point.
If anyone has more similar information, I would appreciate it if you would share it.