1. Sometimes I wonder there is any difference between the two?
I have a several good friends. This is ungrammatical. You can't use 'a' with a plural. You'd have to say 'some'. However, you can say either 'some friends' or 'several friends', but not 'some several friends'.
Would add the same voice or at least hold one of his/her hand for Cool Breeze's argument that with common nouns in the genitive one can leave the article out like these example of his or her and mine?
Let's walk, it's (a) two miles' walk. (Cool Breeze's sentence)