The large collage sample is very similar in structure to the real estate flyer: they are both collections of rectangle cropped images with a single caption. Accordingly, this topic does not repeat the same level of detailed instructions about arranging rectangles and using the precision alignment tool.
With 62 images arranged on a 13"x19" page, however, the large collage does present the opportunity to discuss a few size-related issues that the smaller collage, with only 6 images, does not. In particular, I'll focus on tips for dealing with lots of images, and using the automated sizing and tiling tools to jumpstart the arrangement.
Start a new composition by selecting File/New from the main menu, then use the printer and page setup window to pick the desired printer and set the page to 13"x19", landscape orientation, 0.5" margins all around. Click OK.
Add Images: Select Add/Add Images and select the images to add.
Add Image Tip 1: When you add lots of images to a composition, things go faster if you add as many as possible each time you use the select images dialog, with an ideal of adding all images at once. Assuming that you have left the large composition settings at their default values, each time you add images there is a chance that Easel will change display resolution and reload all current images, causing a delay (it depends on image size, but a good estimate is that Easel will do this every time 10 or so images are added). In the best case of adding all 62 images at once, however, there will be no delay because Easel knows and adjusts for the final size of the composition upfront, before loading any images.
Add Image Tip 2 / Product Plug: Easel's companion Image Browser makes it much easier to find and add the images you want, because it is geared to viewing many images simultaneously and is Easel-aware. With Image Browser, you can page through thumbnails, adding them to Easel one at a time with two clicks, or better yet, by selecting them as you go and adding all selected at once when you are done.
Cropping: It is always best to crop your images as soon as you add them, getting rid of boring background and giving each close to its final aspect ratio, before starting to arrange things. Each time you add a batch of images, they will be cascaded from upper left to lower right. I find it most efficient, working from the bottom of the stack, to drag each image up and to the left; grab its lower right corner and enlarge it; crop it as desired; then shrink it and drag it off to the right, out of the way.
Arranging: Although there's no reason you need to use them, Easel's sizing and tiling tools can make your life easier when you're working with lots of images. As mentioned in the full discussion of these tools (which you should read, if you haven't already), they can repeatedly resize and rearrange the images to improve the overall "fit," and while they aren't smart enough to complete the arrangement, they do an excellent job getting it started.
Edge Handling: When viewing the sample image, toggle back and forth to see the different effect when edge blending is turned off and on.
Finishing Up: There's no substitute for aesthetic judgement and compositional skill in the process of finishing up a complex collage, but Easel's precision alignment tool will help you execute your decisions quickly and precisely. Full information about PAT can be found in working with the precision alignment tool, and a detailed example of using it can be found in the real estate flyer example.