Photos are not going to be in wrong categories as I know I wrote that coppermine script along time ago and its been used alot.
If your photo 1 was in a category id of 3 with a name of sample category it would still be photo 1 in a category id of 3 with a name of sample category. We do a simple grab cat info and insert it. Same thing for photos. Your category id is going to be the same. The photos are all going to be inserted into photopost in the same album id's
Now personal albums are handled differently than regular categories in PhotoPost from Coppermine so that might take some getting use to and lead to some confusion here as to order and display interfacing. I am sure if you compare photo and category id's provided you have not moved anything they should match up.
You could safely rerun an import and it would add missing data but you might get duplicate errors for any data that already exists. I do not believe the importer is going to delete any photos or comments but you can always take backups before you try anything thats always best
As far as bulk options there is a way to bulk move photos from one cat to another but the editing of a specific photos info is per photo no bulk way to edit alot of photos at once.