There is a "gold standard", the classic 4-person RPG party model. It was made by games such as Dragon Age and Original Sin, even in Neverwinter Nights they usually had a party with 4 companions (to get more you needed a special skill if I'm not mistaken)
I personally like 4 characters: the main character and three companions. But there are those who want to change this standard and set up an experiment on the players.
How about 3 party member? This will make our group more united, speed up the battles, and so on. Who has any thoughts on this? The player will not have the feeling that he is leading a small army. How it is done in Mass Effect!