They've got the Falcon 1 and Falcon 9 development under their belts, but this project is going to beat their asses I think. The reusability of Falcon 9 has been overstated all along, and while they'll no doubt improve reusability and shave some more cost, this Starship design is a SSTO, which has literally never been pulled off. Such a thing can be done, but the payload budget shrinks to nothing just to reach SSTO, meaning it isn't accomplishing the intended goal, it just becomes the goal in and of itself.
OTOH, when underestimating Musk, the world has always been wrong, me included.
Staging makes the most sense. A big-ass booster that is reusable to get the upper stages and crew/colonist vehicles to optimum velocity and altitude might Work better if, after separation, continued on a single orbit trajectory, carrying relatively small solid rocket strap-ons to do the deceleration burn after the big-ass booster has done its main job and approaches it's launch site, having circumnavigated.
Of course, the, uh, vision of Musk is to have the SSTO make the interplanetary transit, thus being able to do a propulsive landing on the surface of the Moon, Mars, or other rocky large body. The Mars round trip will take something like four years, which mitigates against the economy of reusability. Having a series of different vehicles looping on their own job makes more sense. Even better is to send the colonists aboard unitary habitats which would ride to Mars, land, and never fly again. That would give the colonists somewhere and someway to survive on the surface.
Musk made it clear that Starship is not SSTO, but he plans to fly it suborbital point to point like an airliner. SpaceX is already advertising for someone to design the offshore launching and landing platforms.
The only people talking SSTO for the upper stage (Starship) were speculating about stripping the landing gear and everything else related to coming back to Earth, to lighten ship. They were thinking of using these stripped ships as habitat modules or strictly for transfers between planets. It might be just possible with no payload and running the tanks dry.
The booster runs 31 engines to put the Starship up forty miles after a four minute burn. Booster and Starship are both reusable.