Backups with Images on External HD

Question

I'm usinge PSE 10.  I do incremental backups whenever I change anything in the catalog and I do a full backup about once a month.  I'm trying to keep my catalogs and backups efficient and therefore my workflow is to keep active projects on my C: drive (images and psd files) and then use the "Copy/Move to Removeable Drive" command to move those images to CD or DVD when I've completed the project.  If I ever need to revisit the project, I can load it back onto the C: drive. What's nice is that this keeps the thumbnails and all the metadata in the catalog, so I have all the details without taking up all the space.  My offline media is flagged with the offline Icon and the Organizer will tell me which CD or DVD I need to search for.  
I recently added a new external USB harddrive (Western Digital My Passport 1TB drive) and I would like to use this in the same way for storing these seldom-used image files and projects.  So my thinking is that when I've completed the project, I use the "Copy/Move to Removeable Drive" command to first COPY the image and .psd file to a CD or DVD, then use the same command to MOVE the files to the external hard drive.  (The CD is simply an emergency backup in case the external hard drive dies).   
The problem is that PS Elements (probably Windows, to be fair) views this new external drive like a "real" harddrive and not like a USB thumb drive.  Therefore, if the new external hard drive is not connected to the PC, the files show up in the PSE Organizer as missing (with the question mark icon) as opposed to being offline like when they are moved to one of the small USB thumb drives. 
So my question is what happens if I don't have that drive connected and I use PSE to do a catalog backup?  I understand that it won't backup the actual image files (which is fine, because I don't want it to), but will the backup catalog still contain all my tags, categories, etc, that are associated with those images, even though it can't find the image files to connect to? 
The reason I work this way is because I really want to use the external hard drive and my CDs as the "image" backups, but I don't want to have to copy thousands of image files every time that I ask Elements to do a full catalog backup.  I just want the catalog backup to save the Organizer database plus all the image files that I'm actively working on.  So, does anyone know if the "Backup Catalog" command will still save all my Organizer catalog database data for those files, even if the full image files (*.CRW, *.TIF, *.DNG, *.PSD, etc. ) are unavailable?  It's asking me if it's OK to skip those files... and I want to say "yes," but I hope it will keep all the metadata for the files in the catalog.  I don't want those thumbnails to suddenly disappear from my catalog after the backup, and I also want the option to reconnect those projects later if I need to revisit that project. 
Sorry for the long question, but I wanted to be clear about what I am trying to do and why.  Thanks in advance! 
-Clem

Answer 1

Thanks so much!  That is very useful information.  If I could request a feature, it would be a way I could tell Elements or Windows, "treat this drive as a removeable thumb-drive" ...or if Elements had a command that if you right-clicked on a photo thumbnail you could say "Treat this file like an Offline File." I guess it would need to be a little less cryptic, but you get my meaning, I hope. 
But you confirmed what I was hoping for... that if I told the backup process to skip missing image files, it would still preserve the fact that they were missing and maintain all the properties assocated with them. 
Their thumbnail is still present in the cache if you have not done any optimization. So if you do a backup, the media files won't be saved, of course, but the catalog will still contain their properties.
Thanks for the tip about the optimize command.  Up until now, I've been thinking that there would never be a reason not to optimize.  But if I understand you correctly, I'll have to remember that optimization can delete thumbnails of unconnected files.  
...one easy thing to do to save everything in your catalog is to find the catalog folder (use the help menu, system info) and do a simple copy of the whole folder and its subfolders somewhere. That can be done automatically if you are using Windows tools like Synctoy.
I agree that a full backup takes time... What is not obvious is how to restrict your backups to your 'active' files. I may have clearer ideas tomorrow morning
I had thought about just making an image copy of the Catalog folder.  I guess I was afraid something would break in the database if it was expecting to see image files and they weren't there.  I know that when you run a full backup from within the app, it saves every image as a unique name and has a cross reference to the "real" file file in the backup .tly file.  I didn't want to push my luck about breaking those links. 
But I do like having a full backup every month or so to have a clean baseline.  What I don't want is a full backup that includes every image file on my external hard drive.  (That's one reason I bought the Passport drive... to make the Full Backups smaller by moving the older project files offline.)
Thanks again for your quick and detailed response!!  Much appreciated.