[itsme]

CSV is meant as a tool for tagging all songs in a fakebook so that they are available to be imported into MSP.
If the usage of CSV files is the only reason why you want to combine your PDFs I would not recommend doing it.
You can import your single song PDFs into MSP and enter your meta data conveniently there. Take a look at MSPs multi select features, they can be helpful. Organizing your files in subfolders and the songs in collections, albums and setlists within MSP can be handled conveniently also with one song per PDF. Lists of songs and their meta data can be exported out of MSP.
If you plan to combine your PDFs for other reasons, e.g. for creating a kind of a fakebook to be shared as a whole I recommend creating a matchng CSV for every combined PDF during the combination process.