You would think that this was a simple answer you have your best man done. But as time has gone on this has changed massively from the traditional one-man best man. Nowadays the number of grooms/best man have grown. I have been to weddings that had one grooms/best man, to weddings that had 12 grooms/best men.
There is also that question does my best man have to be a man. As this has also changed during the years to having a best man to having a best lady. The tradition has always been to have a best man but as times change there are more weddings when grooms are having women to be their best lady. My husband originally started off with two best ladies as he has so many male friends within different groups of friends, he felt that he could not choose one male friend without upsetting so many of his friends.
The decision on who you have and how many you have are completely up to you, when choosing you still consider your budget and how much you are willing to spend on outfits with regards to the number of best men/lady you have. But the many thing you need to consider when choosing men or lady and how many is the fact that you should have those who are there for you no matter what happens in life. That person that no matter how long it has been since you have spoken you know that when you call them they are there for you and most importantly you can have a laugh with each other.