It depends, the stars are based on how good a player is in terms of achieving a teams targets. In your case you will be looking to avoid relegation, a 4 star player is average, if you have a complete team of them you should definately avoid relegation, if you have higher you should be able to do better, if you stay up and your aim is mid table your players stars will decrease.
2-star: don't bother, would be a definite weakness
3-star: might be a decent squad player or backup, but not ideal for you starting XI
4-star: should be a solid starter or rotational player
5-star: should be a good starter who will improve the quality of the team
6+star: would be a superstar for this team
The number of stars a player will get will change each season as the team's reputation and expectations rise .. or fall. So, this year's 4-star might help you avoid relegation this year .. only to be downgraded to a 3-star next season as the team is expected to do more.
that stars are relative to your squad. If you have a squad of world-beaters, your scouts won't find any with high stars. The stars compare what you have in your squad now with potential signings to see if they will strengthen the squad.