1-When making a player a captain does it add anything special to your team ? or it is the same no matter who is the captain ?
No! Team captain don't get anything extra, you can choose who you want, usually most of the managers are going for GB, Best Player or a team legend.

2-Should i consider the foot of player when putting him in a certain position ? it means should i put in DL post a left footed player ? what does it add ? or left or right doesn't matter ?
It dosen't matter because is just for the design.

3-Should i buy defenders and attackers with 1 m 90 cm height or + so they score and defend better with their heads ?
Same like I said above, it won't help you because their height is just for design.

4-Corner and free kicks takers , should i put a left footed player to shoot left freekicks same for corner or the inverse ? or it doesn't matter too ?
Again same story, it dosen't matter.

Good luck!