I'm no expert, but I understand the basic priciples. Holography I know nothing about, but I know interference is involved.

An interferometer works by splitting a wave front into multiple waves, which are allowed to interfere with each other. The patterns formed by this interference are a function of the shape of the object being observed, the wavelength of light, and the geometry of the waves and the interferometer components. Since all of these are usually known ahead of time except the first, the object's shape can be inferred by studying the interference fringes. Michelson and Morley used an interferometer to measure the speed of light about a century ago.

A very simple example: A distant star's light is observed with an interferometer, and it produces a certain pattern of fringes. Now a double star is observed, one so far away that we cannot tell it is double, it looks like just one star. However, it's interference pattern will be different than the first star because the dual nature of the source is encoded in the light and the interferometer can detect it. So interferometers can determine the shapes of objects that are too close to be resolved in other ways.

Interferometers have been used in astronomy for years, the classic example was their use in determining the angular diameter of Betelgeuse.
Light from the star was captured by a large telescope, the beam split into two and then recombined in an interferometer, producing an interference pattern thant allowed astronomers to determine the size of stellar disc required to form that pattern.

The most dramatic example is in Very Long Baseline Interferometry (VLBF) which uses radio telescopes thousands of miles apart on different continents, as the twin "slits" of a planet-sized radio interferometer. This arrangement has allowed us to derive arc-second accuracy in the mapping of radio sources. In most interferometers, the geometry of the instrument is known ahead of time, in the case of VLBF
we do not know the separation of the two antennas precisely, but synchronized atomic clocks allow us to time the different arrival times of the wave fronts, which substitutes for a rigid mechanical structure holding the components apart a fixed distance. As early as the 60s, some ingenious Soviet radio astronomers used direct radio observation of cosmic sources and interfered them with reflections off a nearby lake to substitute for a second antenna!

In general, an interferometer with two telescopes (radio or optical, it's all light) collects twice as much light as one telescope, just as you'd expect. However it RESOLVES sources as if it had an aperture the size of a single telescope with the dimensions of the baseline. So in the case of VLBF, we essentially have a radio telescope the size of the Earth, at least as far as being able to resolve tiny objects. In space there is no limit, since the two "slits" of the interferometer could be hundreds of thousands of kilometers apart, and the two would be connected by a microwave or laser data link that would keep their clocks synchronized, thereby substituting for a rigid structural component. There is no theoretical limit how small an object an interferometer could see at any distance, providing the engineers can just figure out how to build it.