Having "in-between-turns" while nomadic civ (compared to settled civ) would make it easier to run safe, but also give more turns for them to run around and collect some goodies, while settled civs would get more time to spend on actual civ building.
The historical Advantages of Pastoral (nomadic) Civ's compared to their urban, farming neighbors were:
1. No fixed target for enemy aggression - you had to catch their 'cities' first, and as Cyrus discovered, that also meant you had to stick your head out where the nomads could whack it off.
2. More wide-ranging contacts - pastoralists in central Asia, eastern Europe, north Africa, even briefly in North America, had contact with more different civ on all sides, and so acted as 'Middle Men' for trade. Even when the pastoralists themselves didn't have much to trade, they had access to goods that the other Civs wanted, and so got reputations as Traders.
3. Until gunpowder, the pastoral lifestyle meant that virtually every adult male (and a proportion of the adult females) had Warrior skills - could ride, shoot a bow, or use a light lance, and practiced these skills in the course of their daily life protecting their herds. That meant, in contrast to an urban Civ where Warrior skills were practiced by a small elite (aristocracy) or had to be taught at the expense of the economy (taking men out of useful occupations to make them soldiers), the 'nomads' could field relatively large armies very easily - at least for a short time.
4. Almost by definition, the pastoral nomads occupied lands that were unsuited for one reason or the other for a settled agriculturally-based Civ. Until relatively recently (17th Century CE) the boundary line between the forested areas of northern Russia and the treeless rolling hills and flatlands of the 'steppe' was also a sharp dividing line between farmers and herders, and the herders were pastoral nomads. You could settle on the steppe, in well-watered river bottom lands, but you couldn't grow a lot of crops there until the crop plants were modified for dry-land conditions ("Russian Wheat" also allowed planting in similar lands in the American Dakotas and Nebraska, and in the Canadian "prairie provinces', but it wasn't developed until the 18th century CE: before that, planting anything on the steppe/prairie/Great Plains was an almost-suicidal gamble for any farmer). That meant, until post-gunpowder times, there was no population pressure from the more densely-populated Urban Civs. No matter how bad it got from floods, plagues, and crop failures along the Hwang-Ho in China, Chinese were not going to migrate into the Mongolian steppe/desert to live: even without the small matter of a lot of armed Mongols, the terrain and climate simply wouldn't support anything resembling their lifestyle and preferred food sources.
5. As a result of the above, throughout history until the advent of gunpowder began to give the settled Civs an overwhelming military advantage, aggression was almost always by the pastoral Civs against the settled Civs nearby, not the other way around (and Cyrus' disastrous attempt at it gave a very good lesson to anybody else on why such aggression was a Bad Idea)
All of which means, to 'model' a Nomadic Start and give the player good reasons to stay nomadic for a while, the Nomadic Civ should have military advantages in low-cost or 0 maintenance for his troops, ability to 'mobilize' a larger percentage of his population as effective troops, an 'evade' capability for his Settlements/City-Equivalents that makes them very hard to destroy or damage with an Infantry army, and th ability to extract resources - especially food) from terrain/tiles that do not support agriculture until the post-Renaissance Eras of the game.
Of course, the other side of the Nomad Problem is that once the agriculurally-based Civs have access to gunpowder weapons and modified food crops that can be grown on the marginal 'nomad' terrain, their overwhelming numbers of better-armed troops doom the nomads - see the destruction of the 'Tatar' and Great Hordes in southern Russia or the obliteration of the Native American plains cultures. That means the nomad Player has to make a very calculated decision on when to shift the center of his Civ from pastoral nomadic to settled City-based. IRL, that was most commonly done by simply conquering and ruling cities from other civs - the Turks and Mongols for two prime examples.
There is also an 'intermediate' solution shown by the relationship between the Greek city-states in the Crimea in 7th to 5th centuries BCE and China: the Scythian or 'Northern Barbarian' nomads could extract tribute and essentially treat the settled cities as 'Suzereigned' in Civ VI terms, getting all kinds of goods and services from them that the pastoralists could not manufacture on their own.
IF a game can put together all these features: military bonuses, ability to use marginal tiles, ability to profit from Trade that doesn't originate with them, ability to extract advantages from neighboring cities or civs, and finally, ability to designate a settled capital after conquering such a city, then we could have a very viable alternative to the traditional Civ pattern of Settle At Once Or You Cripple Yourself that has been the norm in every Civ rendition since Civ I.