You have options here depending on what you want and how you set up your database...
"I would like it to show up or maximize in its own window when I click on it."
If you store the picture as a reference (The path to the picture's physical location is stored.) You can open the picture with your computer's preferred application for that file type simply by double-clicking the field.
You can also create a second layout with the container field sized to be the larger format you want and you can script a button that uses the New Window command to open a new window and switch to this layout. You can learn more about "New Window" by looking it up in filemaker's help system.
"how do I make one main image, but also have a series of secondary images in the same container field?"
Well you can't, unless you use an image editing program to create a new picture that merges them all into a single picture. You can, however, create a related table of images and display them in a portal. You can add/remove images for a given parent record by adding/deleting the portal records. If you look up "Portal" in filemaker's help system, you'll find some fairly decent explanations on how to create and use portals.