I'll try to answer your questions, sorry if it doesn't satisfy you. I cannot delve into detail about the lives of its inhabitants, though I can give you a rather general picture of it. I'll mostly talk about late 18th to mid 19th century

Northern Black Sea Steppe and Dobruja

The Northern Black Sea Steppe frontier region roughly spans from the Pereskop Isthmus at the Crimea, to Bessarabia, down to the Dobruja region past the Danube river in what's now Bulgaria. Many travelers and officials described this region as mostly barren, sparsely populated, and desolate. In the 1830s, intense summer heat and freezing cold winter prompted French and American economists studying Russian policy in Bessarabia to call it "The Land of Death." Severe heat accompanied the summer highs of 35–40ºC; severe frost and hailstorms also accompanied its winter lows of –15 to –20ºC. Traveling through here is also very harsh and difficult. The lack of bridges forced travelers to rely upon ferries or crossing through solid ice of winter to cross rivers. Strong winds from the south across the steppe also made travel dangerous and difficult. Horse-drawn carts and carriages often broke down, got stuck in the mud, or stumbled in deep holes on poorly maintained roads. Wood, water, and forage were generally unavailable in a 13-km radius extending from the fortress-town of Ochakov and recently settled peasants were sometimes forced to travel 25–30 kilometers to find their nearest source of water. Peasants who lived here tilled the lands and deliver their goods to markets with pack-animals, usually imported Bactrian camels which, combined with the vast steppes gave travelers the impression of Central Asia. Cossacks garrisoned in this region also trafficked black market goods from the Danubian Estuary.

Down to the Danubian Estuary, things were starting to look a bit more lively, as the estuary made an important site of trade and smuggling, populated by all kinds of people from merchants to fugitives to fishermen, all generally wished to live away from state interference, be it Russian or Ottoman. The Danubian Estuary and the ports of Bessarabia are a haven for smugglers and criminals, all of them experts at navigating through the waters of the Black Sea Coast, evading Russian, Wallachian, and Ottoman authorities. Trafficking black market goods and human cargo is a principal and lucrative business in this region. In return for cash payments, bands of Zaporozhian Cossacks organized the transportation of migrants across the Prut River into the Principality of Moldavia. Migrants also paid boat captains to safely and secretly transport their families from the Bessarabian to the Moldavian side of the Prut River. Those who aren't dabbling in illegal business are mostly fishermen and aquaculturists.

Finally reaching the Dobruja region, the place was mostly dotted by towns, small villages, or agricultural communities. Helmuth von Moltke in 1839 once estimated the population as less than 20,000 in total though I think this is an underestimation since Ottoman censuses later point the population reaching as high as 200,000 inhabitants (though it could exponentially rise thanks to Ottoman resettlement program). Being a migration corridor from Istanbul to the South and the Black Sea Region to the North, Dobruja displayed an astounding ethnic and cultural diversity. An Ottoman census of ten kazas (judicial districts) in Dobruja counted Turkish, Romanian, Tatar, Bulgar, Cossack, Lipovan (Old Believers), Greek, Roma, Arab, Armenian, Jewish, and German families settled in Dobruja. Later migrations also added Circassian Muslims to the population. Compared to Bessarabia or the Danubian Estuary, the Dobruja Region is relatively economically and socially stable, thanks to close proximity to the Ottoman capital. This also meant that the region is a prime target for migrants, especially Bulgarians, Romanians, and Tatars from the North. The Ottoman authorities were generally receptive of these migrants, seeing it as a way to increase the economic and agricultural value of the region. By the mid-nineteenth century, Dobruja has become a rather important economic center of the Empire, producing foodstuffs for the Istanbul market and wood valued by Ottoman architects, engineers, and shipbuilders.

Moving on to other parts of your question, it is true that military conflict, political rivalry, and the physical and psychological dislocation messed up many individuals’ identity and loyalty. This is why the more "frontier" regions of the Black Sea Steppe like Bessarabia are rather lightly governed by authorities. Entrepreneurial frontiersmen promised debased oaths of loyalty and dubious pledges of military service in exchange for social and political autonomy. Cossacks were rather famous for this, as both Russian and Ottoman officials complained how the Cossack “scoundrels” and “deceivers” were slow to respond to calls of mobilization or straight up refused to show up at all.

Soldiers also defect rather quickly. A rather famous frontier tale of this region recounts how three cossacks serving the Russian army were captured and incarcerated by the Ottomans, were set free, lived in Istanbul, served in the Ottoman army, and finally re-enlisted (toward the end of the war) in the Russian army. Renegade Russian soldiers and officers served in the reformed Ottoman army, and conversely, Ottoman military officials and provincial governors often found refuge in the Russian Empire. In the first few decades of the 19th century, Crimean Tatar returnees from the Ottoman Empire enlisted in the Russian army and fought against Ottoman troops. And in the Russo-Ottoman War of 1806-12, Crimean Tatars and Zaphorozian Cossacks banded together and attacked the army of a rebellious Ottoman governor despite their shared enmity.

Inhabitants also fluidly adopted identities best suited to their needs. To gain access to the lucrative Russian market, Ottoman merchants often attempted to pass themselves off as Russian citizens using forged documents purchased in the black market and flying Russian flags. Skeptical of the long-term loyalty of settlers from the Ottoman Empire, Russian military officers refused to provide travel and identity documents to migrants seeking temporary residence on Russian soil. Bulgarian migrants in the Russian Empire preserved their Ottoman citizenship for as long as they could. When forced to renounce their allegiance to the Ottoman Sultan in exchange for the right to remain permanently in the Russian Empire, many simply returned to the Ottoman Empire.

Religious conversions were also a very common response to the changing realities of the Black Sea Frontier Region. In the Russo-Ottoman War of 1806-1812, a certain Ottoman soldier named Ahmet Bey deserted to the Russians and petitioned for assistance to convert to Christianity in order to cleanse himself of “Mohammedanism.” In response, Russian General Staff in Bucharest directed Ahmet Bey to consult with an Orthodox priest in Turnovo to learn the ways of Christianity. Upon completing his training, Ahmet Bey was to be settled in Odessa and became a Russian subject. The converse is also true, Russian soldiers converted to Islam during and after the Russo-Ottoman War of 1828–1829.

Finally, territorial sovereignty is something that both the Ottoman and Russian states expended considerable energy to in order to territorialize, demarcate, and stabilize their control over the Black Sea region. However, this is something that proved difficult for both states, prompting it to be called by Russian administrators a “wild field” (dikoe pole). Despite the establishment of well-marked Russian border posts and the construction of well-defended Russian lines, in the early 19th-century Russian administrators continued to use ambiguous terminology when referring to the Russian territorial position in the region. Eventually, the Danube Estuary river zone became a defining dividing line between an imperial core and a northern frontier periphery, turning into a fixed border between the Ottoman Empire and the Danubian Principalities of Wallachia and Moldavia.

In conclusion, life on the frontier zones of the Black Sea Steppe Region is quite harsh and difficult, proven by how few permanent inhabitants in the zone. Travelers and military officers from both sides described how desolate and sparsely populated the region was. The region for most of the time became a zone for travelers, soldiers, migrants, or merchants. Most of the more settled inhabitants are either in Wallachia, the Dobruja Region of the Ottoman Empire, or past Bessarabia in the Russian towns of Ochakov and Odessa.

Sources:

Migration and Disease in the Black Sea Region: Ottoman-Russian Relations in the Late Eighteenth and Early Nineteenth Centuries by Andrew Robarts

The Black Sea: A History by Charles King

“Towards the Character of Ottoman Policy in the Northern Black Sea Region after the Treaty of Belgrade (1739)” by Aleksander Halenko

Warfare, State and Society on the Black Sea Steppe, 1500–1700 by Brian L. Davies