Your arena is fine. I would even consider building more before moving up to DIII. My minimum arena that I would want before promoting into DIII would be 12000/3500/500/35. Adding salary would just take away from your weekly profits. Once your arena is set, you can start stockpiling the cash you need to promote while you train your trainee.
Your issue with your ticket prices is not your seats. You need to lower your ticket prices for your LT, Courtside, and Luxury Boxes you will fill more. buzzer-manager.com has a tool you should check out that helps you set your arena prices. The next price change on Tuesday so do it tomorrow or Monday asap.