Thanks Richard. i think I need to read this a few times to understand it completely. I find the negatives bit a bit confusing. Surely I want the images copied over, that is the whole point of the exercise isn't it?
This was the point of my initial question as to whether you want to keep your image files physically separated for business and personal, or whether this is a purely organisational question to do with Catalogs only.
If you wanted to manage your physical storage (say) in a strict date structure - that is what I do, letting LR do everything automatically - this storage arrangement need not reflect that one image is imported to Catalog A and another is imported to Catalog B; a third image may even be imported to both at the same time and it will not make any difference.
The files could all just stay where they are, if you want.
A little like: one person is a member of the Police and his/her service-related information appears in police records; then becomes a member of the Army and now starts appearing in military records; but throughout all this, the person's home address, phone number etc is all just recorded within the same common public systems as anyone else's would be.
OR, a soldier may live in military barracks apart from the general population, and where he /she lives would then not appear in the same listings as a police officer's home would.
You could adopt a setup where you have two separate trees of folders to accompany two separate Catalogs. In that case you could leave the folder arrangements inside each one, much the same as now; or you might decide to move toward different kinds of system / folder naming entirely, within each "stream", to better suit possibly different requirements - though LR tends to reduce the significance of this whole aspect in practice, due to collections etc.
I sometimes get the optin to back up my catalogue and usually do this and have today. If i start to muck about and get something wrong will this backup still be there of alll my images and info connected to them?
"Export as Catalog" makes no change to your current setup whatever. "Include negatives" copies files if selected, does not copy files if not selected, but the physical images referred to by your live catalog are not themselves affected either way. The LR thumbnails and edits etc that you have selected to export, still remain in place also.
So the only problem comes when you start deleting/removing images afterward: you need to establish whether something is now a redundant file since it has been safely duplicated somewhere else (which is fine to both delete and remove), or the one-and-only file which the Catalog you happen to be in does not require, but which a completely different Catalog still does require (which is not fine to delete, but OK to remove).
This problem does not arise if you haven't "included negatives" since you are then not duplicating anything (except database information); there are no redundant physical files anywhere; and therefore there is no physical deleting to be done. You just (in this scenario) Remove the database entries in your working catalog, which relate to the classification of image which you have just exported.
Still backup all your physical files as well as your Catalog before starting any of this!
And always reconsidering: could I manage to separate these images well enough in practice, within the one Catalog, anyway? (though if you later do find these two catalogs unwieldy, you can re-merge them then using "Import from Catalog").
First, decide whether you want to store your image files separately too.
Also, backup everything!