My way: sell older and players who are weak in progress.

Prefer to buy medium strong players. With luck, 3-4 players per season is good for further progress.
Funding ingame is done via world cup, mostly. Other funds are much lower.

FOR SALE: DC-13skill, ST with low marks, or slowest progress. MC too. 3-2-3-2 is my line so i do not keep much dc/dmc/amc.

Injuries: I have problems with MC line. Had with DC, then 2 season only 2 injuries, lot of yellow cards, total random part. Invest in stadium.