They would start with a hub that is 78 meters wide.
The National Space Society has the goal of 100-meter wide space station that weighs 8500 tons. It could house 500 people.
The 8000 person Kalpana stations are thus thicker than the proposed Gateway Foundation spaceport / hotel but they would have similar diameter.
I had described how if 160 double sized Kalpana space stations were built then 2.5 million people could be housed in space. 2.5 million people is the population of the USA in 1776.
The Orbital Assembly videos describe a pathway that would lead to the first large 18000 person colony.
Orbital assembly describes a reasonable system of welding modular segments and then using flying space drones and crawling space drones to move pieces into place and to further weld segments together.
Modules would be used to make hubs and then to make the outer ring and then to add thickness with more modules.
They have selected the main construction material of magnesium nanocomposite for lightweight and strength. There have already been tests of electron beam welding.
They want to use seven layer bora silica glass for the windows. This was used for the ISS (International Space Station) capola window.
Icarus Interstellar had a proposal for 10,000 person worldship. However, the habitation ring of the ship design could have Bigelow Aerospace inflatable modules attached to a basic frame.
The proposed worldship had 40 modules that were 120 meters by 155 meters.
Less room but still highly useful would be to use Bigelow BA2100 modules that are already designed.
Bigelow has 2100 cubic meter modules designed that are 18 meters by 12 meters. Cruise ship rooms are about 60 cubic meters. A Bigelow BA2100 module could have 15 rooms each. Half the space used for hallway and other purposes. 100 BA2100 modules could comfortably hotel about 1,500 people. Less room is needed for temporary stays than for long-term colonization. The first megabase would be for a more crude hotel and to house people to work on industrializing space.
A SpaceX BFR could launch two BA 2100 modules at a time.
About 70 SpaceX BFR launches could be sufficient for an initial 1500 rotating station.
Priorities would be to establish better in space construction and in space assembly.
The SpaceX BFR seems like it might be ready by 2023. This will likely be ahead of proven large-scale space construction is established.
The beams and materials for construction can thus be brought up with SpaceX BFR cargo delivery.