If I select iCloud Photos and Download Originals to this Mac option, will the full-resolution originals be stored on my Mac and in iCloud?

See the following from Set up and use iCloud Photos - Apple Support

Your photos and videos are stored in iCloud exactly as you took them. All of your images are held in their original formats at full resolution — HEIF, JPEG, RAW, PNG, GIF, TIFF, HEVC, and MP4 — as well as special formats you capture with your iPhone, like slo-mo, time-lapse, 4K videos, and Live Photos.