With regard to the difficulting in spinning a structure for simulated gravity, there are several issues that would need to be resolved, including transporting or erecting a structure with a sufficiently large spin radius, providing sufficient impulse for spin, balancing the structure during spin operations and during spin, and navigating and orienting communication antenna during spin.
The minimum required spin radius is quite large compared to the size of payloads that can be delivered to orbit using conventional launch technology; around 20 m. This is based on both the physiological response (vestibular effects) and the psychomotor response (disorientation from objects behaving differently under gyroscopic motion and centrifugal radial pseudo-acceleration than under gravitational acceleration) that have to be considered. The physiological effects are easier to assess objectively, while psychomotor effects may vary dramatically between people. The effects depend on rotation rate, with <1 RPM giving no significant physiological effects, and >2 RPM considered a general threshold for continuous rotation (though some sources differ). There is relatively little experimental information on these effects in a practical space-like environment, though fairly extensive human testing has been done in a terrestrial environment. According to one source, the minimum rate off rotation and radius for normal human function is 6 RPM with a 14 meter radius, giving 0.58 g acceleration (Thompson A.B., 1965, Physiological design criteria for artificial gravity environments in manned space systems, First Symposium on the Role of the Vestibular Organs in the Exploration of Space, 20-22 January 1965, US Navy School of Aviation Medicine, Pensacola, FL, NASA SP-77, pg 233-241). Assuming a 2 RPM rate, you would need a 220 meter radius of rotation to achieve ~1 g acceleration, which would obviously be very large in comparison to existing spacecraft, though reasonable on the scale of a large permanent space habitat. This scales linearly, so you would get ~0.5 g at a 110 meter radius. If we could tolerate a rotation rate of 5 RPM, we could get 1 g at a radius of about 36 meters, or 0.5 g at 18 meters, which are somewhat more reasonable, though larger than any unitary spacecraft that might be launched from Earth’s surface.
Spinning up such a system would require a substantial impulse (K = 1/2Iw^2) which will be substantial for a large payload, and therefore require additional propellant, both to impart rotation at the beginning of the trip and remove it at the end. One could avoid expending propellant and make it possible to recover energy at the end of the trip by using a counterbalance flywheel, but as this would have to have the same magnitude of angular momentum (with an opposite spin vector) it would be either very large, very heavy, or both. It would also be necessary to provide fine balance control during spin to avoid precession and nutation effects, further complicating the system.
Spinning the craft using a counterbalance mass or having dual craft attached by a tether would be the most simple system. However, this means that there would be no inertial (stationary) portion of the craft at which to mount observation or communication systems. Maintaining communication links and using stellar navigation in a constantly rotating system is very complex. A more complicated system that would have a non-rotating hub and spinning hab modules would be preferable, but substantially more complex.
From an experience standpoint, our most applicable experience was the spin experiment on Gemini XI, where the Gemini spacecraft was tethered to the Agena upper stage and slowly spun to achieve a ~0.02% of Earth gravity. So we have no practical experience with constructing or operating large scale spun spacecraft or habitats. We do frequently spin smaller spacecraft and satellites for stabilization or to ensure even solar heating, but even this is often complicated despite the fact that these structures are essentially rigid (except for liquid propellants) and can be spin-balanced prior to launch. A large habitat-type structure that cannot be spin balanced and may have moving masses within it is several orders of magnitude more complicated and well outside of current experienece in space operations.