The Oort clouds extend out approximately to distances believed to range from 0.8 to 3.2 light years and if this is the same for other stars and the average distance of separation for stars in the vicinity of the solar system is six light years. An asteroid habitat at the mid-point between stars will be three light years (on average) from either star, and barely within the upper bound estimate for the outer reaches of each star's Oort clouds.
A mobile space habitat could harvest resources from the icy planetismals and cometary bodies in the extreme reaches of the overlapping Oort clouds. Their ability ability to convert matter into usable energy will be an important limit on their capacity to survive and thrive in deep space.
The question of available energy resources for interstellar habitats has been considered by Eric R Jones and Ben M Finney's "Fastships and Nomads: Two Roads to the Stars" 1. Their model interstellar habitat is comet-based, but the energy issues are the same. Comets are mainly asteroids with lots more dirty ice.
The greatest obstacle facing potential nomads, is energy which is very
scarce in the interstellar deep. Nonrenewable sources would include
deuterium to power fusion generators and the kinetic energy (energy of
motion) of the comet, which could be extracted from interaction with
the galactic magnetic field. Renewable energy sources would include
starlight collected with gigantic mirrors and possibly cosmic rays (if
anyone can figure out a practical scheme for catching them). Elsewhere
we have estimated that the aluminum in a typical comet would be
sufficient to build mirrors to collect a few hundred megawatts of
starlight. Other more abundant substances may prove to be more
applicable for the mirror surfaces. We expect that power levels of 1
megawatt (MW) per person are reasonable and therefore a typical comet
could support a few hundred people with starlight.
The use of Bussard technology to collect hydrogen as a resource is probably going to be limited by the amount of power required to drive such systems. Because of the low relative velocities of nomadic habitats to the interstellar medium hydrogen would have to be collected by first ionizing the gas and driving it towards the habitat with vast magnetic fields. It seems likely that two sets of magnetic fields would be used to push the ionized hydrogen together. One magnetic scoop would be based on the habitat itself, while another scoop was situated at a distance and this pushed the ionized gas towards the habitat's collection field.
The main drawback would be the power necessary to implement a dual collection system. If the energy extracted from the hydrogen exceeded the energy cost in powering this Bussard double collector, then it would be feasible. This is speculative.
Jones and Finney are confident that sufficient energy can be extracted from starlight, the habitat's kinetic energy, cosmic rays (speculative), and nonrenewable sources like deuterium to make small spacefaring communities in the interstellar deep viable.
1 Ben R Finney and Eric M Jones (eds) Interstellar Migration and the Human Experience (Berkely: University of California Press, 1985)