Each brand has their own particular brand of card and the number of photos you can store depends on which card you are able to use. I choose high resolution for all my photos - you never know when you'll want to print one. The low resolution option gives you lots more photos per card, but isn't good for printing. You can always upgrade your camera, or purchase additional storage cards. Plugging in the cables every time you need to download your photos will aggravate you in the long run, so build in the cost of a download device when purchasing your camera.
Optical zoom is the real zoom, using the camera's optic lenses.
Digital zoom merely crops in the same photo to a specific area of the subject material and won't offer the same clarity. You just register, upload, pay a small fee, and your prints will arrive in the mail, all ready to put in your album. A digital can really be the best of all worlds once you learn how to use it. It can act as a Polaroid in the sense that you can see your prints immediately - no sending off film to develop. You don't have to pay for processing, but you can still get prints if you want them, and frame-quality, too.