one issue per thread!
Your first suggestion is not a bright idea - clever users who know the coppermine structure can easily guess the url of the full-size pic if they know the thumbnail url. You could use the deprecated ssi.php script that doesn't respect permissions and therefor does exactly what you're up to.
Your second suggestion isn't possible due to technical limitations, yet you can use custom thumbnails as suggested in the docs.
Marking your proposals as "turned down" - the first suggestion won't be helpful for most users, the second one can't be accomplished.