It's good to believe in your players, but...
They all have a low potential and will all cap out very soon. They're fine players, but in div 2 I assume only 1-2 of them would be an average starter.
About training, you do it double position. It's fine now due to the low potential of your guys, but hiring a level 6 trainer for this is useless.
I don't think it's worth spending more seasons in div 3 for a bunch of allstar guys. Superstar potential is the minimum to make it worthwhile in my opinion.
2.5 millions is nothing. It's a mountain for a team that hasn't seen anything higher than d3. However, that's what I value to be THIS season benefice for me.
Your arena is big enough to get a lot of cash if you promote. You can already build it up to ABBL standards, but what would be the point? It's taking a long time, you could do it much faster.
To give you an idea: if I demote this season (which is probably not gonna happen), I would get around 3 millions by selling a couple of players. I'd get a good draft pick and train him along with my other young boys who still have a good progression margin (and are already better than the d3 standards).
So again, I respect the fact that you want to win with your current roster. Just be aware this is not the best solution and that sooner or later you will have to sell most of your team if you intend to promote and stay up. Maybe you could consider selling some boys and buying 3 MVP rookies with good starting skills. That would make your training worthwhile and you could plan long term. Although I know you do not like trading at all...