As many as you have in your golf bag.
It is unlimited
As many as you want.
In accordance with the rules, you are only allowed 14 clubs for a stipulated round of golf. This is only for official rounds of golf, if you are just playing a casual round of golf you can carry as many as you want.
You would find that a tour pro would use between 12 and 20 golf balls for a four round tournament.
What clubs are suggested to carry in a golf bag
106 golf balls
== == You can carry as many golf balls as you want.
A tour pro would have around a dozen golf balls in there bag per round, just in case. But it is completely up to the player.
356,000 million golf balls ;)
Approximately 5 golf balls could fit.