It's difficult to really assess the well-being of the general population in the absence of direct sources and historical data : however, it is generally assumed trough archeological evidence that population in Gaul, in spite living in a period of important social polarization and degradation of free and semi-free peasantry into a broad "humble" social class, was overall better fed than during the last centuries of the Roman Empire before, and until the late Middle-Ages (if not the XIXth century in some aspects). Nothing fancy, especially as the decline of the monetarized economy and international trade kicked in, but also seemingly more varied than during Antiquity. : peas, grain, beans, turnips asparagus,fruits and gathered vegetables most of the time with the relatively common consumption of eggs, milk and more rarely and depending on one's social and geographical situation) meat (often pig and beef, but also mutton or goat which sometimes supplanted them, and horse meat in various proportions sometimes up to 15%).

You're right that nobles (either coming from the military elite of Franks or Roman aristocracy, both tending to mix early on) were, would only by sheer contrast and the absence of a middle-class, living a much more fortunate life than the majority of the population. Essentially, they kept late ancient culinary habits, including its grande cuisine with all its display (ducks' tongues with chestnuts with their side of turnips with lard, for example) to the point a dietary treatise was written by a Greek physician named Anthimus for the king Theudeuric I.

De obseruatione ciborum is interesting because it orders all available food : bread; various red meat from farms or hunting and their offal; drinks (honeyed wine, absinthe wine, beer and....lard?); white meat and giblets; some preparations (quenelles and a recipe with poultry and an ancestor of floating island); how to prepare all sorts of eggs (with a great care on how long they should be cooked and advising to eat only the egg yolk and only as a preparation); fishes and seafood (with a mention of salmon soufflé); then vegetable (essentially the same than described above) both as meal and as seasoning; leguminous; dairy products (and flour, due to a meal made out of milk and flour against dysentery) and, finally, fruits; with regular recommendations (eat rice for diarrhea, garum is a big no-no in spite of its ubiquity in Gaul, well cooked meals are the pathway for health as a first "digestion",etc.)

To give you an idea, there's a quote on chickpeas.

Chickpeas are good, if they are well-cooked up to the point they begin to truly melt and if they're seasoned with oil and salt. They're approved for kidneys too. If, at the contrary, they're raw, I absolutely advise against eating them, even to healthy persons because they're causing damageable flatulence, digestion trouble and belly disorder".

The Merovingian noble is certainly well-fed (with not so uncommon obesity), and not crudely so, with some of them being true connoisseurs. The Carolingian capitulari on agriculture (such as the famous De Villae) eventually from Merovingian era practices, giving them a new structures and institutionalization. This nobility was marked by its display of wealth, power and Frankishness (especially North of Loire, and critically if their ancestors weren't part of the old, itself romanized, Barbarian military elite), by adopting the social codes attributed to Franks in fashion : Barbarian names, carrying weapons up to the grave, for the nobles closest to power harboring a ring in the pommel of their swords (the "Lord of the Ring", or the "ring-giver" being the ruler giving away rings symbolically biding him and his truste), basically a whole "identitary set" that could be considered as "bling" when it come to jewelry (Barbarian looking, but probably and until the VIIth, mostly made in the Eastern Roman Empire from Indian gems). To quote Bruno Dumézil, Merovingian Franks were Romans pretending and convincing themselves they were Barbarians; all of this happening in a continuous meting of various identities, interests, opportunities, etc. with redefined and renegotiated cultural, political and social apparatus.

(taking from this earlier post)

As for where they lived, you're right that they still lived in villae, but although they would be familiar enough to a Roman observer in being both a productive center and a prestigious housing, there would be some differences : wood, cob and bricks dominated in most of Gaul (although stone building were still made in the southern third) since the IVth century
Besides the main buildings master room, the aula, which served as a hall/court/reception room, there were bedrooms and a chapel (or a place of worship), and probably rooms for service or some other everyday use. Outside, there were additional building for the extended family and domesticity, craftsmen and servants. Royal or princely palaces had buildings to house officials, treasury and baths. Across a palisade with open wooden (and sometimes decorated or painted porticos), the scattered houses of peasants that worked the immediate demesne could be found.
Frankish nobles, their truste and their children might probably have mixed up with servants or peasants more or less regularly but contrary to Anglo-Saxon households where the hall and others rooms were rather made in separated buildings mixed up with work places and the like, the social-spatial differentiation in a Merovingian villa might have been much more obvious in costume and power relations.

The aula, an hall of reception probably covering both floors, feast and social display was, embellished as far as the owner could afford with tapestries of silk (or, barring, lined or wool), a great focus on luminaries (Franks were among the first to use glass panels on windows), probably mosaics (Late Empire having been sort of a golden age of mosaics in western Europe) and all sorts of decorations displaying their noble activities and Frankishness, all of this being covered a roof made of tiles or slit. The furniture was made of metal chairs, tables, potteries, painted cups, etc. But as well furniture that would have been considered as normal by Imperial and Late Imperial Romans, but exotic and obtained trough long-range trade such as African tableware, Constantinople's tapestries or silverware from the central and eastern Mediterranean (which became hard to get by the mid VIIth and the decline of Mediterranean trade).

Villae weren't necessarily the only noble housing in Francia, episcopal and patrician housing and palaces still being found in cities (themselves still richly decorated and furnished), but they represented an important feature of Merovingian noble life and urban palaces are comparatively less known due to the lack of historical and archeological sources. In Paris, the late Roman Palais des Thermes seems to have been used by several Merovingian kings, as described by Verentius Fortunatus and possibly coupled with a fortified palace at the rough emplacement of Palais de Justice, the ensemble benefiting from the same assets than aforementioned villae. Still, the moving Merovingian courts were rather electing the countryside as their favored lifestyle, and cities monumentality and nobility are often marked by the episcopal power and display (bishops themselves being often members of powerful local families) and their relation to this new urban power.