How modular is the Genesis Starliner, does it have the ability to function similarly to multi-role ships such as the Constellation? Or should we expect a ship more similar to a Reclaimer, that's focused largely on a more defined role?

The Starliner is designed in compartments so that its interior can be very modular. The limits of the chassis mean it probably won't be especially effective in some roles (such as offensive combat missions) but there's plenty to build on for careers beyond just passenger runs. The role of the ship is primarily set to be a cargo ship (personnel cargo), but with the various variants planned it should support multiple roles.