4. If you bought a children’s lantern, you’ll want long-thin slides for it, not the large squarish ones for adult lanterns. Children’s slides are almost all small, but they come in many different sizes, so measure the height of the slide slot on your lantern and be sure the slides you bid on are the right size for it.
Adult slides come in Wood Frame (4 x 7”) and “Economy” (3 ¼ x 4”) with no frame, and English format (3 ¼ x 3 ¼”). All will work in your lantern, but for the Economy and English format slides you’ll need a “slide carrier,” also available on eBay. See below.
Don’t necessarily go for a complete slide set initially. An assortment will generally be less expensive. The slides may have some torn bindings and scratches. That’s OK for your budget, but avoid slides that are broken or badly scratched. (A good rule of thumb is to always buy the best you can afford.)
For a large lantern, you might start by buying single-slide examples of the many different types of slides—photographic, illustrated, songs, movie advertisements, etc. Make a list of what you want, budget your money, look for examples with a low starting price, and bid your budget until you win.
Another approach is to focus on a particular subject that interests you. Fishing, golf, sewing, art, music, an area of the world, etc. etc. If it existed in 1900, there are slides about it. Search eBay “Completed Items” for “magic lantern + ______” to get a sense of what’s out there. Some subjects are very collectible so you’ll have to figure out what you can afford, and perhaps settle for less desirable examples.