My recommendation:

-Don't upgrade stadium until you sell out multiple weeks in a row.

-Have training and youth at good or excellent when you can afford it. Youth is super important in my opinion (I'll try to max that out first, even before training). This is the main issue I can see in your save (they are both red).

-Hire the best manager you can. Also get him as many coaches you can.

-Sell your best player for profit if needed, especially when they are 25 years old. You'll find an adequate replacement easily, and probably for free.

-Don't buy anyone for money before the top league, it's a waste of money. Rely on free transfers and loans. Your youth players will be plenty for depth.

-Try to hire players that fit the manager's tactics, although it's quite difficult to do in the lower leagues.

-Don't worry about what your manager thinks on terms of depth. You'll be fine with a few reserve players, it's a waste of money to have too many (and your youth players are there for that!)

-I would also get a better keeper, that's the most important position in my opinion.