download full resolution photos

Photos is a "non-destructive" editor. That means that when you crop or annotate or edit an image, the original file isn't changed at all. Rather, Photos stores in its database the steps used in the editing and, when you ask to see it, Photos recreates the edits on the fly. So edited pictures are not kept (except for thumbnails and some previews used to make things faster.)

The original pictures are kept inside of the Photos Library package, which is (with some effort) accessible with Finder. But going inside the "package" risks confusing the database so that it may not be able to match up originals with edits and such things. Messing around inside the Photos Library package can be very bad. If you insist, then use a copy!

One thing that is changed for the originals is the file name. You can't find your picture IMG_0022.jpg. With multiple cameras there could be bunches of those, and there would be massive confusion in addressing them. So every image file is stripped of its file name and assigned a new one that is so long and arbitrary looking that it will be unique. But, of course, Photos records the original file name in its database.

If you want the original picture, then you can choose File>Export>Export Original, and you get exactly the original picture back with original filename and metadata, and with no comments or editing.

You also said: I need get them as JPGs. I'd also like to see what size they are and what kind of resolution they have and what format they end up in..

If the original was a jpg, then the file will be exported as jpg, but if the original was a tiff, then that will be the format of that file-- the original isn't changed.

Resolution, format, focal length and other metadata can be found in the Info Window within Photos (⌘-i). Also, when you export the original using File>Export>Export Original, full information (of the original) will be available with metadata readers, like ExifTool Reader. If you use File>Export>Export nn Photos, then you can control jpg quality, file size, image size in pictures, and color system.

Photos are in the Photos App and stored in your photo library where they are accessed by the app. Your originals should download in the background over time.

All photos are stored in the photos library file. You can select an image in photos and use the get info command for details from the menu bar. You can export unmodified originals , or export the image as is with any changes you apply, from the menu bar.