1. There is no "exact" answer, because the DB size is dependent on leagues running, players retained, managers nationality etc. Suffice to say that the difference between small, medium and large is a huge amount of players (starting and regens).
2. Again, sorry, but it's a combination. There might be a more precise figure available if you compare an exact amount of leagues to a certain database.
Also keep in mind that a low detail level in the game can help you speed things up.
I'm curious though why you want answers to these questions? If they are relevant to your machine, then people can offer more advice if you post your specs.
Good luck gaming anyhow