Can I delete images that are sitting there from old listings? If I do so will they no longer show on the stuff that is still for sale in my store?

if the images are still being used in a listing, then yes deleting them will cause them to not show up when person views the listing.

if the listing they were used in is no longer active (not being relisted, etc) then can delete. Otherwise, you'll want to keep them.

thank so much!

Ok so how can I put them in something manageable?

can use the folders feature under manage images to keep them sorted