As Oxygenum stated, albeit rather confusingly, you HAVE to manage
GS (since you cant manage stamina other than training) better bud. Having been in your league and a witness as you made 3 straight Finals appearances, I know you can. I don't know what's going on currently but it isn't as big of an issue as others make it out when your not attempting to compete. If you are training with no risk of demotion then screw GS but if/when you push for promotion again you have to focus on it and I'd suggest practicing in the mean time. :)
As Lawrenman stated, keep Bello. I'll amend that though and say IF AND ONLY IF you are going to train him. It appears he's gotten zero training since drafting him and that's a pure waste. Get what you can for him or incorporate him into your training. On this point I agree with lawrenman.
I highly disagree with him about Cortes though. You can easily make a team 7-8 deep with 20k-ish players and promote out of D.IV. Cortes isn't impressive offensively (barely 38%) but he shoots well on assisted shots so just make sure you get a passer and he'll keep you afloat. More importantly, he's only given up 2/17 shots all season. Lawrenman is delusional if he thinks you'll find a 10k player that wont absolutely suck offensively that can defend that well for you. Play him off the bench in a 3-bigman rotation and his lack of offense won't matter much but you also won't lose leads you've generated when he comes into the game.
Improve boxes. Build 5 more. (80,000) Set price to 600.
Improve Court. Build 100 more. (200,000) Set price to 70.
Lower Set price to 27.
Bleacher. Set price to 6.
Pretty much agree with this one across the board.