My wife roped me into this for my girls 1st grade class. 21 students are doing self protraits in art class and I'm supposed to make a poster. At first she just wanted rows kind of like a yearbook page, but that is kind of boring, so maybe a collage. But for a collage, that is a lot of layers and to try to get them all on I think would be impossible? Yes, No, think it can be done? I thought about going with a 27x40 size to get the most area. What do you think on size? Would like to hear your take on these questions and your thoughts in general on this project
You might try scaling down the project first to get the layout right. Use copies of the images and work at 25% scale or so. Then, work on the individual pictures separately, saving and closing each image as a separate file. When those images are done, open a new canvas at the actual size of the poster, paste in your smaller "layout" image, scale it to the larger size and use as reference as you open each individuals shot and paste in position.
This way, you are using as little resources as necessary on this large project.
I hope this makes sense. I can do it a lot better than I can explain it!
Ed
If you want to go real easy, I saw that costco.com does 20x30 poster collages for $9.99. I don't know how much creativity you get to input as I only saw it this morning and it isn't something I was really interested in. I think you can add up to 30 pictures.
Mark