To build and run a charger network you need people for at least these things:

• To design the stations (including the charging equipment (hardware and software), landscaping, buildings)

• To manufacture the charging equipment

• To decide at a high level were to put stations, and at a lower level to find specific sites, buy or lease those sites, and go through whatever legal process is needed to be allowed to build there.

• To deal with electric utilities to get power to the site.

• To do the actual building at the site, including preparing the land, maybe paving, installing the chargers, hooking up to the incoming power, putting up signage, etc

• To maintain it. It will need regular cleaning and trash pickup. Someone should be checking regularly for problems that won't be found by whatever remote monitoring and diagnostics they have. When a problem is found, manually or by there remote monitoring, someone has to go fix it.

• To provide customer support.

If you do all of them in house you need a large team. But a lot of them are reasonably done by hiring another company to do them in which case you might not need a large in house team.

I'd guess that they do the first (design), part of the second (assemble the charging equipment from components they have custom built by other companies), the high level location planning.

I'd guess that the lower level part of site placement is done by local firms familiar with the area that Tesla hires, that dealing with the electric company and the actual building is done by a local general contractor and whatever subcontractors that general contractor uses.

I'd guess that the cleaning and on site checking for problems is handled by a local maintenance company. Fixing problems would either be a local company or someone Tesla sends depending on what it is that needs fixing.

Customer support would likely be Tesla.

If Tesla considers that their existing Supercharger station designs are good enough to continue using for a long time for new stations, then they might really only need to keep in house the high level decision of were to put them, charger repairs, customer support, and hiring the local companies that do the field work.