I worked in Paris for two years. My advice:
Pensions etc. are OK, the employer should organise it. Mine is with AG2R La Mondiale and I’m looking forward to finding out what it’s worth when I retire.
Accommodation: difficualt to find flat shares in central Paris because only the former maids’ rooms in the attic or basement are available, meaning there’s room only for a single or a very close couple. It’s said that over 50% of Parisians live alone.
French people are only too happy to tell you how things should be done, to the point of driving you nuts.
Medical care is good but you’d better have private insurance for the topup bit.
And yes, lunch arrangements will be good and the food excellent.
Best advice is to try to find accommodation within walking or cycling distance of the office.