Well right now it is the summer holidays until I think the beginning of September. There is 5 people in my group and we have decided to do a comic project however we don't know how many pages of the comic we should do? How many do you recommend?
It depends on how long you guys want the story. A normal chapter is usually 22 pages long. I've seen some people do 24 or 18 pages for a chapter though. Comics that are only one chapter are called one-shots. Other people like to do their comics in overall long arcs of story plots. I think it would be best for you and your friends to first write a script and do some story boards of how you want to go about this comic. Once you have a structure of how you want to tackle it, you can then figure out page numbers.
Plenty of comics have chapters that are regularly 40+ pages, the 22-page "norm" is common in weekly manga and monthly American comics, while longer chapters are common in graphic novels and monthly manga.
Don't worry about chapter length if you're not working with a publisher's requirements! Make your comic as long as the story needs to be, and split the story up into chapters where such a split feels appropriate.
If you're just starting, I recommend doing some short one-shots to get the hang of telling stories visually.