Is there an ideal proportion you need to use if you want to expand your arena?
I mean % Bleachers, % Lower Tier , % Courtside Seats, % Luxury Boxes , ... ?
No, but you should try expanding sections that are selling out on a regular basis. I see you're adding 6 luxury boxes, and it may be a very long time before you need to add more of those.
Your lower tier and courtside seats, however, are full every single home game, and they've been sold out since the 2nd of February. I would recommend expanding those as soon as you can afford to do so.
The rule of thumb I regularly espouse on arena expansion is to only expand by about half of what you can afford to expand, thereby leaving some money sitting around while you wait for those new seats to fill up.