Megastructures vs. real planets. Should interstellar travelers live onboard giant megastructures or land on the planets?

When we think about the space colonies we are facing an interesting problem. That problem is:  should we colonize planets or use megastructures for making those colonies? There are many good things on both of those roads. 

The planets already exist. And they don't require so much work as artificial megastructures. But megastructures are fully controlled things. Their gravitational fields can adjust by adjusting rotation speed. Another good thing that supports megastructures is that they are sterile. 

There is no hiding micro-organisms in those artificial worlds and that means there are no so big risks in those artificial worlds. In some visions, the people who live in those artificial worlds can control advanced robots on the planets that they see during their journey. And that thing decreases the risk. That is the interplanetary and interstellar missions. 

The fact is that when we think about the interstellar- and interplanetary spacecraft's size differences we can say that interplanetary spacecraft might be 200-500 meters long if they operate in Jupiter's trajectory. But if spacecraft operate at Pluto's orbitals and Kuiper's belt their length could be about a kilometer. The interstellar spacecraft will be a size of a minimum of 5-10 kilometers or even larger. They need to support their crew in any possible situation. 

The large size of interstellar spacecraft is necessary. The reason for that is there must be lots of equipment. And that crew requires their privacy. So those spacecraft will be like Stanford Torus. They involve an artificial world with gardens and villages. So interstellar spacecraft will be megastructures. And the crew can live onboard those gigantic spacecraft. 

Interstellar flight is far more difficult than interplanetary flight. The craft must be independent. And there is a need for more than one craft for cases. That there are technical or social problems. That means there must be some kind of evacuation place for the crews. 

And that means their AI must have complex and effective datasets or databases in all kinds of situations like head injuries or some other very bad things. We know that even the best medical people cannot know all kinds of operations. 

The AI must have datasets about many unusual surgical operations. The fact is that even the best teams forget their skills, and if there are no accidents in a long time, that means those medical operators cannot practice their skills. 

And then if something unexpected happens those people cannot operate because they have no practice. Even if there are no problems during spaceflight when the crew wants to land on the planet. Their feet may slip. Or if the planet has a similar atmosphere as Earth another problem is biohazard. If some organisms are released on board those spacecraft that causes a horrifying situation. 

The main problem with hypothetical interstellar missions is time. And the second main problem is if something goes wrong. There is nobody who can help if there is some kind of problems with technology or social relationship. That means those spacecraft must equip with systems that guarantee the success of the mission.