i think these are mainly decisions for GMs (and potential story hooks!) rather than items of canon. i haven’t read all the CB published material, but in what i have there doesn’t seem to be any indication of whether or not the Nomad ships have minotaur engines or not. based on technological primacy, very possible for Bakunin and Tunguska to have them, less likely for Corregidor given its start as a prison. fwiw, even if they did have minotaur engines, the motherships might very well still travel along the circulars rather than burn their own fuel, as docking fees are probably cheaper than burning your own nessium.
for the Circulars, it’s implied that they have minotaur motors as those are required for interstellar travel. given the fact that they are essentially space trains that are also giant cities on fixed travel routes, i think their dimensions and specs are deliberately left vague for the GM to fill in detail if they want. perhaps the C8 which hits the Human Edge and Svalarheima is more cargo heavy and less developed than the C6 which hits Neoterra, Varuna, Acontecimento, and Yu Jing systems. i don’t recall the passage, but my understanding is that they circulars don’t stop, they merely slow by vila boosters to a pace that allows for intrasystem ships to dock with them and ferry people on- and off-board.
in terms of gravity, there are few passages from the core book and GM guide that specify the hows for particular ships:
The drive-pillars on Bakunin are generally kept firing at all times except for short-lived periods of “turn-over”, generating a default state of artificial gravity in which “down” points towards the magnetic exhaust nozzles on the “bottom” of the mothership.
Corregidor prefers short, hard burns for manoeuvring. (Visitors will note that most areas are outfitted with crash couches.) Thus the mothership is usually kept weightless, and the interior environments largely reflect that. Where gravity is needed for certain industrial applications, however, individual sections of the station are designed to be rotated for artificial gravity.
Experiments in synthetic gravity have had mixed results, and no examples have been more than proof-of-concept tests with highly classified results. Thus, the matter of microgravity environments is a concern for those travelling in space, as it can lead to significant health issues. Treating these problems is within the capabilities of modern medicine, but it’s still better to prevent them in the first place.
Some vessels resolve the issue at least partially by orienting their decks so that the ship’s engines are beneath their feet, so that when the ship moves, its acceleration serves as a substitute for gravity. Other vessels use centrifugal force, generated by rotating the ship along its axis, to replicate gravity. Others still use diamagnetism to simulate a gravitational force, though typically at less than 1g due to power consumption. These solutions don’t work equally for all ships in all circumstances, however, so the search for a better solution continues