They really don't steal things anymore (as in, the original concept was their state-supported efforts to steal things ended by YE 33), assuming they ever needed to. If other Freespacers were charitable enough/easy enough to persuade to join them, they'd never have needed to steal anything, so they'd have no reason to be a neutral haven for criminals in the present day, either. That'd change a whole bunch of things.
The '99.9% of their imports and exports are stolen...' figure includes the material brought by the initial defectors who founded the colony. If gear brought in by immigrants who didn't technically own it isn't included in that figure, it probably goes down to 40% or less, even before considering the possibility of other (sub-)factions outright giving them foreign aid, which could reduce that to almost nothing... maybe a few accidentally stolen pens.
They definitely wouldn't have literally stolen any ships from non-Freespacers. It's hard enough for them to operate their own technology., and, well, other factions aren't pacifists with a relatively low tech level, so they'd get shot to oblivion, if they tried!
The only way for them to pick up ships from other factions is if those ships fly into the system unprepared, get hit by a solar flare, and then get left behind in a stable orbit, or relatively undamaged at a crash site on the outer gas giant's moons, without being scuttled or recovered. I'm not sure how likely that is. I would like them to have at least one scout ship about this size, regardless who made it, though.
I assumed their food would be grown in hydroponic farms, mostly on the outskirts of Newtown; acres of pressurized habitats using chemicals refined from the mining ships, recycled organic matter, the local clay 'soil', 'sunlight' provided by lamps powered by the colony's fusion reactors, and the local water supply to grow vegetables, lentils, seaweed, and other conventional plant-based foods in elaborate patterns.
I can add mention to their diet when going into more detail about their culture, here, if it's feasible, and also add more information about the farms to the planet article.