I'm no expert, but your arena looks ready for D3 but your roster doesn't. Anyway, your odds of promoting seem pretty slim to me because Hawaii Chopsaki and Chaos Titans both probably have a considerably stronger team than you right now. If you are trying to promote relatively quickly, I would stop building my arena and focus on either player acquisition in the transfer market and/or an expensive trainer (whatever your preferred strategy is). If you are content with a slow climb up the BB ladder, sure, keep spending to build that arena up to 20k, top divisions potential.