Visa exempt. 2 visits a year by land and unlimited times by air.

It’s the duration of stay each visit which may cause problems

It’s always up to the airline. If they refuse to return you then you have to fly back on a flag carrier

No fine but stamp. Unless you pass the border before 27 midnight

Yes you can get readmitted .. make sure you have an onward flight and be prepared to get asked for travel purpose

Depending on what you are consulting you might be able to qualify for a smart visa (T) as a "retired" expert.

You need to show a service contract with 50k / month income and the company that hires you needs to be in a specific category.

Smart visa holders dont need a work permit, and don't have to do 90 day reports (its yearly for them)

Fly is your only option with 2 land crossings.

Air Asia. CNX to KUL

VOA cannot extend (7 day "extension/denial" does not count as one)

If you plan on staying for 60 days, obtaining a tourist visa is actually cheaper and a bonus of not dealing with the immigration office at all.

The south korean citizen does not need to do anything.

Some immigration offices are open for that purpose. Otherwise Monday

Usually new passports (with no stamps) attract attention by any border officers. Because it shows you are trying to hide something or may be not a genuine document, so they look deeper and tend to do more investigation and see if your story checks out.

They are just asking standard questions that any border officer would, don't feel offended. i.e. What do you do, why do you visit, how long, etc