I foresee hollow protoplanets!
Since this species develops in a free-fall environment within a space-based cloud of gas littered with resource-rich/-poor asteroids, the first major structures will be built on the asteroids for mining operations. Individuals rarely want to travel long distances to get to work (long is, of course, relative in space), so housing will be built on the same asteroid as the mining facility. As the facility grows, it will need access to more resources, so either the company will start another mining facility or haul other asteroids to an existing one.
Clumps of asteroids then become the foundation for larger settlements, which attract more attention, more business, and more inhabitants, which bring in more asteroids to support the growing population.
Independent facilities will produce a similar effect, though in this case "clumps" will be individual asteroids connected via trade routes. The collections will attract attention, which brings in business, inhabitants, and more facilities. To prevent unwanted drifting, asteroids would be tethered together to emphasize established trade and transport routes.
In either situation, the city is developing in three dimensions, expanding roughly evenly in all directions. 788
This produces a spherical structure, with the oldest buildings at the center.
Tethers and nuts and bolts should be quite capable of holding things together; after all, they do quite well under constant gravitational stress from Earth.
The common architecture is going to be something much like what's on the ISS. There's no real down direction, so doors can be in any flat surface, possibly even in cones, corners, or hemispheres. In the case of asteroid clusters, paths of travel will be delineated by the structures themselves, where walls and solid connectors work together to create tunnels through the whole structure. In the case of asteroid collections, paths of travel will, in the macroscale, be defined by the inter-asteroid tethers, while local conditions will be like those for asteroid clusters.
The tethers and pipes used to connect structures and asteroids can double as infrastructure. Tethers can provide electricity and fiber optic cable. Pipes supply fresh water and remove waste.
(All of this ignores the viability question of your scenario, which I am in no way capable of answering.) 99