[itimpi]

1). No - there is no easy way to add just a few books - you always need to generate the complete catalog. There is an optimisation option, however, that you should use so that Calibre2opds only updates the catalog files that have changed. This makes a big difference if syncing to a remote server. Make sure, therefore, that you have not selected the option to disable the runtime optimiser on the Main tab.

2). Not quite sure what you are doing here? My guess is that you exported the books from the Calibre library. This would cause errors as Calibre2opds relies on the files being stored in the exact relative paths specified in the Calibre metadata database and exporting the files changes their names and thus breaks this relationship. A copy of the library created in such a manner is bot a valid Calibre library. When you copy using Explorer then the filenames are preserved. However copying every file is rather slow so you may want to use a tool such as FreeFileSync or SyncToy that only copies changed files as that is much faster. I personally use FreeFileSync when copying to my backup libraries.