Have you given any thought to the background for the asteroid belt? Are the characters new to the entire system or just the belt(s) itself?
If it is like the Wild West, then you are probably going to be limited to small "towns" (i.e stations) spread throughout the belt where miners come to sell, to refit and repair. So your stations should be set up to support such a thing. These stations might be free-floating, but you could also incorporate things such as larger asteroids that have been hollowed out as a result of mining and a ramshackle town has taken up in it, with crazy corridors, docks and airlocks stuffed all over the place at random. Or you could have more orderly purpose-built stations. Perhaps the orderly are the mining companies, and the disorderly are the people who just decided to set up shop there. You might then find even smaller (family sized, or say up to 100) habitats anywhere else around the belt, in all kinds of shapes, sizes and configurations.
You probably are also going to have other mining facilities - smelters to extract the ore, refineries to make the metals, perhaps even some small fabrication yards that take the raw materials and construct some industrial items in the belt before they get shipped off somewhere else. Depending on how you want to do it, you could have "fixed" facilities in a standard, regular orbit, or you could have large industrial ships that float around and have a gang of mining ships that bust up asteroids and tow them back to the refinery.
If its a rich belt, you probably are going to have lots of traffic - mining ships, ore barges, tugs, etc. You could add in lots of patrol ships if its high-law, or since you describe it kind of the wild-west, maybe its more of a no-man's land, where every ship travels armed and/or with escorts. In that case you could have pirates who prey on the weak, or mercs who will attack other miners for the right price, claim jumping, maybe even get to the point where the sheriff and his deputies show up in the system and start wiping out the bad guys.
there's all kinds of possiblities, and ships to go with them! If its the frontier you can pretty much go with standard designs, but also just cobble something together like people on the frontier would since they have limited access to shipyards and the like. Plus people are going to salvage and re-use what they can. An asteroid belt can be a fun place to be sneaky, building asteroid fortresses, habitats, disguising missile batteries and turrets in hunks or rock.
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