I'd do the buildings first before any expansion on the stadium, you don't get much ticket income at the beginning of the game and you don't have a large fan base.
You should aim to sign 5* players, whatever level you play at, theres always going to be selling and buying players, there is no point in buying 4* players because when you level up, you will have lower level managers bidding on these players because they would see that player as a 5* when you see it as 4*, you should easily be able to pay player wages.
no i wait until day's games are over and train the remaining squad down to 60% condition so they can be near 100% for the next game.