we figured out large scale and pressure vessels already
No. This is an assumption not borne of physics or engineering. There is no magic material that will make large scale pressure vessels suddenly viable. It (and space elevators) are mathematical constructs, not real things.
Use this calculator. checalc.com/calc/vesselThick.html – punch in 15 psi for pressure, and 100F for temperature. Play with your pressure vessel. Wall thickness of large scale habitats will need to be many metres of solid steel (or equivalent material). Even if you magically mass produce carbon nanotubes or something, you still need hundreds of millions of tonnes of carbon to pull off any large scale vessel. Your talking about ingesting entire asteroids just for building materials. You don’t launch that shit on an interstellar journey.