It will take you a lot of time figuring out how much you have to spend for increasing you arena. Further you have to adjust it all the time.
In general I recommend to set up the prices at about half of the maximum allowed per category. That means for bleachers ~10, lower tier ~35 and so on. If you do that and the specific category is still sold out you can add seats. My arena is among he biggest in my league and I do make more money with tickets than better teams with smaller arenas.
Since you are only Div 4 with a lot room for improving your team it wouldn't hurt to make the arena a little too big for now since you'll probably get more fans withing the next few seasons.
Thats the way I did it and never have regret it.