Some tennis related questions?

I’m watching tennis at the US Open at the moment and i have some questions.

1. Do the players have to pay for their tennis-outfits and -rackets themselves, or are they provided for free by their sponsors (I ask because some are using multiple rackets and outfits per match)?
2. Where do the women put their (2nd service-) balls?
In their pants or in a specialy designed device (they never seem to lose them while playing points)?
3. Why does the net have a ‘dent’ in the middle?
4. What happens to the old balls after they’ve called for new balls after 7 games.
5. Does the grunting and screaming/shouting really helps the (mainly women) players to put more power and/or conviction in their strokes?

Well, that’s about it.
If you have some or one answer, or a question of your own, be my guest and put it out there!
Thanks in advance.