It is unlimited
The PGA do not approve golf balls, the USGA and R&A rules committees do. They both publish a list of conforming golf balls.
Yes
The Professional Golf Association (PGA) of America has 28,000 members but only a select few of those play in the PGA tour.
Nothing. They can legally be played on the PGA tour.
tytlist
The PGA is the Professional Golfers Association in Golf.
well there are many different types of golf balls some are expensive and some of them are dirt cheap. the different brands of golf balls is hard to know because some are being used which you havent heard of. i say though on the PGA tour around about 10-15 different brands of balls are used. Examples, Nike, Callaway, Bridgestone, Srixon, Titliest, Top Flite not (flight) and many other brands of golf balls are being used which i probably don't know about.
A Titleist Driver can be purchased at many golf stores. Here are some of those stores 3 balls, Golf Galaxy, global Golf, PGA Tour Shop, Golf Locker, Amazon, Ebay, 2nd Swing, and Fairway Golf USA.
Professional Golf Association
As many as you like...
PGA CHAMPIONSHIP