I think about:
9000
5000
500
40
good plan for my arena? :)
Definitely very bad plan ;-)
At least before promotion.
There is no sense to build 5000 lower tiers in 4th division because it seems impossible to fulfil so many seats in Your league. Keep in mind that the lowest possible price for lower tier ticket is $ 18, it's still quite expensive in D.IV.
I think it would be hard to sell 5k tickets even in 3rd division (in fact I have problem to sell 5k lower tiers even in 2nd division when I lost previous game although my price $ 21 is close to minimal). And even if You sell so many seats then additional profit is very low because it's difference between price for lower tier and for bleachers, so it isn't $ 18 but maybe $ 10. And real profit is still smaller because You need to lower price for whole sector, not only for new seats, so Your profit from old seats is smaller.