I second Ramquizibo on this. Promote!
When you promote you will get a great deal of cash from your arena incomes and promotion bonus. 
Personally I have a goal of promoting every other season if possible. I would suggest you follow that strategy. 
BTW you have some awesome trainees with very high potential! Good for you

Your arena size is very big for Div IV so its a good size for Div III. Check my newbie guide if you need ideas for Div III. 
GL in the finals!