Size measurements are very important for correctly identifying relics, but you gave us none for your seven objects.
Object #1 appears to be a fancy women's clothing "cut-out" stamped sheetbrass button, Victorian era (late-1880s-to-early-1900s.
Object #2 is a button too corroded for certainty in identifying -- except I'm sure it isn't a Military button.
Object #3 does not seem to have a button-type of attachment on its back.
Object #4 is (as you thought) a World War 2 era (or later) US Army collar-insignia disc. Having "clutch-pins" on its back means it is from no earlier than 1942. But the rest of its back is too corroded and concretion-covered for me to be sure whether it is from 1942-45 or from 1946-70. You can go to the following webpage, study the photos and info there, and make your own decision about the time-period of your collar-insignia disc.
Dating Metallic Insignia: Collar Disks
Object #5 is a brass tack from furniture or a trunk. It could be purely decorative or it could be a "skid-disc."
Object #6 is made of iron and does not seem to be a button.
Object #7 is (as you thought) a ladies' shoe button-cover, from the very-late 1800s to early 20th-Century.