I don't use photoshop often but am not clear on image resizing. I am wanting to make a photo collage of images similar to the below. I will need to play around with scale a bit using the transform tool but I am not sure whether this reduces the quality each time I scale the image up. I don't have or know exact dimensions of each image its more a matter of figuring out at what scale it looks good.
I've had a look at the below tutorial about resizing images but I don't think its quite what I need for what I'm doing.