Most Efficient Rocket Configuration

So if you are going to Sergeaa, you way to be as light as possible and save fuel. Load your lander parachutes and you won’t need any engines to land on Sergeaa. Taking off is a whole other story. You would need like another station in orbit already because it is hard enough leaving sergeea’s atmosphere.

Well that depends. On a vacuum engine you will want maximum nozzle length and minimum nozzle throat size. For chamber pressure there is a sweet spot that depends on the mass of the craft and how many engines there are. You'll probably want pressure fed or electric power cycles depending on how far your craft is going. Electric for shorter distances, pressure fed for longer distances (pressure fed increases delta v but way has less thrust than electric, so plan accordingly).

Altitude engines are really hard because it depends on what target you have for them. You can have a thrust focused engine, an efficiency focused engine, or a mix of both. For a mix of both, a full flow staged is your best bet with the smallest nozzle length. Throat size and chamber pressure depend on the size and mass of your craft.