Background: In a society where human beings have lived among the stars for tens of thousands of years, they would have accumulated a lot of junk, so they just decided to throw a lot of it onto uninhabitable rocks near colony planets for easy disposal. Kind of like the galactic version of a landfill.
My characters are salvagers, meaning that they go down to these junk planets and bring anything remotely valuable back with them. I want their base to be very large but still mobile. Most of it would be taken up by containers of junk they collected, things to be sorted to see if they're valuable, and things that are valuable if recycled in large quantities. Essentially most of it is just a series of large compartments that act as warehouses, with some recyclers that are either advanced and run by actual people (metal, antiques, jewelry etc.) or very basic and run automatically (pipes, structural supports, broken concrete, etc.).
I want to know how big such a ship could get, because that will tell me how much junk they can handle at any one time and give me an idea of how profitable they would be. It would also give me an idea about how large to make the crew, since my characters only make up roughly twenty or so of the crew.
Currently the ship is roughly the size of a small moon, just a little bigger than Deimos.
The main constraints I already know about are: mass, acceleration speed, construction, expense, and landing.
Mass and acceleration are sort of tied together. It takes a energy to accelerate and decelerate in space, and the more mass something has the more energy is required to do so. I want to know how much energy such a thing would take. Do I need to create a new energy source for this in order to make it feasible? And is hand-waving the energy source acceptable? Acceleration for this ship doesn't really need to be all that fast, although it does need to be able to travel between solar systems in (at most) a month or so.
The construction of the ship would've been enormously expensive, and it would've had to be constructed in space from the outset. No way is it possible to build something that large on a planet. Possibly a shipyard that manufactures everything and puts it together? I was thinking that perhaps asteroids and uninhabitable planets were pretty much looted of all their ore, and then the ore was refined into metal that the shipyard uses to directly build the ships. Seems reasonable, provided the technology is there. The cost to build and maintain the ship would be enormous, but since my characters are mostly low-level grunt workers, I can probably explain it away as the corporation paying for it.
Finally, since there is no possible way such a large ship could get close to a planet without causing a potential apocalypse, let alone land on it in order to salvage valuables. Destroying the very valuables you are there to collect by your very presence is a major issue. So, the ship would probably need to have a hangar that can send shuttles down to carry the cargo back up. They wouldn't be small due to the large cargo area, but it would at least be possible to land on planets so they could gather the materials.
Did I miss any major problems? Should I make the ship smaller?