No, they are not based on the actresses, and I have plans for Minerva. Don't worry I am going to do something about her age and looks before adding her.

Dumbledore even use magic or tricks on his proxy to forge the contract.

Dumbledore use ministry to force him by saying it is for resurrection of old family and made a contract which makes him impossible to go out.

In this story they never met before and he is never interested in other houses, so he don't know about them.

No it is not copied. There is some similarities at start but not entirely same.