RE: Writer's Lounge
The first time I've read the first Shark Wars book, the main character and his best buddy as you should call it, they were swimming one day in the ocean and then the author just jumped ahead and introduced the other 4 main characters, right away in a group as they were swimming by.
For me personally, although the book was action-packed and funny too, I just felt that the author rushed it a little when he made the scene that the characters just instantly met each other and the dialogue feels a bit rushed too, the characters having too much "faith" in their saying. If you know what I mean by "faith".
I really hoped that the author was going to introduce the characters one by one through a conflict that they themselves couldn't go through and then the two main characters come and rescue them from their misery.
In my opinion, don't do what he did(even though I really liked the book and became a fan). He rushed through the meeting of the characters which may create some stereotypes about each one.
It's up to you if you want to introduce all at once, but one thing I learned when planning and writing a story.
Writing a story is the same as making and preparing food for a person.
They would want to savor each bite they get and not to rush it, or they will become sick. It is the same way with stories. Don't rush it, or risk getting your reader confused and put down your writing.
Try introducing the characters a bit and show their current situation and let them play around a bit, let the reader to get to know them more to avoid stereotypes.
You can also introduce them through a conflict and let that be the focus of the chapter but like everybody else says, don't do it if it doesn't have any connection to the main plot!
Hope this helped you!