One of the most important things to consider, at this late stage of slide projector life, is the availability of slide trays. Probably there are more Kodak Carousel trays available than any other brand, as this was the industry standard for projectors in the USA for many decades. Also, Kodak made a stack loader that goes in place of the tray, and it allows you to project a stack of loose slides without putting them in a tray. You can also find third-party high quality projection lenses for just about any projecting application you might have, in addition to the standard Kodak lenses. There were also dissolve units to control a pair of projectors to dissolve between slides, synchronizers to sync an audio-tape narration to the slide show, etc. A complete system. The Carousel/Ektagraphic line of projectors were made for so many years that in the beginning they came with high-wattage tungsten bulbs that generated a ton of heat, later they were replaced with lower-wattage quartz integral reflector bulbs that gave the same amount of light output with less watts and less heat. It would be best to make sure your potential purchase is new enough to have the more modern bulb type. While camera stores sell projector bulbs at enormous prices, there are on-line bulb vendors that have much more reasonable prices.