If you plan on sticking with FTM software, keep them separate. I have found that the software starts slowing down when you hit about 2000 people in a database and gets progressively worse as the number of people increases, especially if you add media or sources to your database. If you just want to record names and dates and use another software to manage your sources, then FTM can handle more names.
Frankly, I gave up using FTM after experiencing one too many instances of the software shutting itself down. Also be warned, if you use the description field for any of your events and later want to share a gedcom file or move the data to another software, FTM merges the description and place fields into a single PLAC tag in the gedcom. This is a HUGE mess when uploaded to other programs or even back into FTM.