Staying in 14th Arr. 5 nights in Sept.

the biggest problem in the 14th is that there are a lot of Breton creperies

5 km is a long way fro the Luxembourg Gardins which are kind of on the edge of the 14th. Where exactly are you talking about staying. We have spend a couple of weeks near Edgar Quinet, the cemetery, the brasserie on Blvd Montparnasse -- lovely area -- but also about a km max from the Luxembourg Gardens

That's not possible. It's 2.6 kilometers from the Jardin de Luxembourg to the Porte d'Orléans, the furthest southern point in the 14th.
Nonetheless, it's a bit further out but you have a tram at the southern edge, as well as buses and metros

It's a fine neighborhood with nice places to stroll/dine/drink with the locals, but it is fairly quiet. Not loads of tourist sights over that way unless you have Catacombs & Montparnasse on your list of To Do's.

The guy who does The Earful Tower podcast recently filmed a YouTube video on the 14th a couple months ago. He lives in Paris with his family, but has created a series of YouTube videos where he picks a different Arrondissement to explore and spends the night in a local hotel and provides highlights and info about what the neighborhood is like as he walks around filming stuff. Just search YouTube for The Earful Tower and you should be able to find his videos if you want to get a sense of what the 14th is like.

Back in 2018 we stayed near Alesia metro in the 14th at both ends of our month long trip.
I loved the area.
My impression was that we were in "real" Paris rather than "tourist" Paris.
Easy access via public transport throughout the city.
Stayed in a nice little hotel and ate very well locally. Shopped at small businesses.
We did walk up to Lux Gardens, which seemed very popular with the locals.

It says .5. Not 5. hard to see the period.
Hotel Istria by Magna Arbor

29 Rue Campagne Premiere

Oh that's a good location! No issue at all, still quite central.