We'll be transiting from a RST ending in London to another RST tour starting 5 days later in Bayonne. We plan to spend the layover in Paris, some of which we've seen on a previous BOE 21 day tour a couple of years ago. We're coming in on a Monday via train from London and plan to leave from Gare Montparnasse early on Friday morning to reach Bayonne via TGV several hours before our tour begins the same day in Bayonne. Making the early train out of Montparnasse is critical. We will be using local public transit for all travel. Any suggestions/cautions about staying very near Montparnasse? Also, any suggestions for sights to see? We're planning the Louvre, Montmartre, Eiffel Tower, Arc de Triomphe. Are all easily reachable by transit, with some walking, from Montparnasse? We did get to see several non-Louvre museums on our BOE trip.
Edit: Not really worried about terrorism. More about local crime hot spots excluding pickpockets. Also if we would have good access to transit, especially in evenings, from most any tourist area in Paris to Montparnasse.