Like in ksp explore and do stuff better!

The posibility of having múltiple command pods , space station modules like labs or habitats, and bases , also maybe astronauts

I feel this would add more realism to the game, and produce an extra challenge for building rockets

With the community of modders that is out there, things such as planets or more parts of the same category are not really necessary, but there is a lack of gameplay mechanics to explore. Things such as electricity, Life Support, Malfunctions, Automated procedures, LIFT, just in general more mechanics to consider when designing or executing missions.

It would be good to have more modules for space stations etc. also collecting science like in ksp would give more purpose to sandbox

Then you can have an Apollo style mission ^+^

You can already do this.

1 design your spacecraft
2 add a docking port where you want your rover to be
3 design your rover and dock it with your spacecraft by either building an infrastructure with wheels and struts so you can dock it before you leave smearth, or dock in orbit.

I did a mission to mars and I used 3 command module's one was my spaceship I used for orbiting returning to earth etc. Another was a Lander that I used to land on mars and return to orbit. And the last one was a rover that I brought to mars docked to my Lander and undocked once I landed.

It sounds stupid but if you wanted to land on smoon, then ditch a control pod attached to wheels (a sort of rover) then fly the actual craft just like normal and the "rover" remains just like any other active craft you have on the same mission.

This would make base building/space station building more fun

For example:
Base Module the main base module shaped like a command pod

Living module shaped like a 400 fuel tank

Retractable greenhouses/living modules like in KSPs base module.

Have different sorts of payloads and capsules for different purposes eg large capsule containing an object to put into orbit. Or a small capsule containing a rover you can deploy by itself. Etc