I have 128,000 citations to 4500 sources, and don't see any performance issues. Maybe you have many more Sources? I suspect that if they came from your Ancestry tree each Source that's cited multiple times, like census, appears as a separate Source in TMG. If every citation creates a separate Source I can see that the MSL would be a problem.
You can find the people linked to a Place entry in TMG by selecting that Place and clicking the Events button. That produces a list of event tags using that Place with the Principal(s) listed.