I 100% agree that getting rid of Himzo is a solid option.
However, I believe that keeping your older guys is fine if you can get yourself a trainer with Career Extension. I've found this ability useful, as it allows me to get the most out of players in their mid-late 30s. These players sell for much less than guys 32 and below, but can definitely work in this division. My strategy when I was competing against you guys was two position training 6 forwards and having 2 guys (no younger than 35 usually) at each of the remaining positions.
As far as training, 18-19 year olds with all-star+ potential should be your trainees. Even a star potential player is good enough in D4. I'd suggest a lvl 5 trainer minimum. I did have a level 6 trainer for a season though.
I kept my ticket prices at their default price and expanded my arena to 10-15k while in D4. I literally just doubled then tripled each type of seat.
Have an idea of what offense you want to run and what you need to make it successful. Compare your teams stats to the teams you struggle against and upgrade your roster as you see fit. For example, I noticed I was struggling against F&L, Wild Dogs and your team on the boards. I got myself a player with 16 on rebounding to plug up that hole. Also because I only trained driving and jump shot, my forwards were a defensive liability. I got myself a guard with 18 outside defense to fix that.
My strategy is still centered around my forwards and shooting guard taking care of the offense with the guards and center taking the bulk of the defensive responsibility. Although for whatever reason, despite him having very low inside defense and shot blocking, my forward Robby Cosby gets me a couple blocks a game. That helps. I've run base offense for the past few seasons after Motion and RNG couldn't get the job done. That was probably because of some roster holes though.