What is your evidence that Musk has "engineering skills"? Nothing in his background would suggest that, and the internal reports we've heard is that other people in his companies are doing the engineering and Musk doesn't know what he's talking about.
It's a fukking idiotic idea, and his claimed justifications for it make no logical sense. He simultaneously claims that he wants to colonize Mars as a buffer for human survival, yet also claims he wants travel between Earth and Mars to be as easy as a cross-country trip. If people are constantly traveling back and forth between Earth and Mars, then how would Mars be a buffer anymore? Environmentally it's a horrible place for humans to be due to its distance from the sun and comparative lack of gravity or magnetic fields, you'd get more of a "buffer" from setting up colonies in Siberia and the Australian outback than from putting them on Mars.
Half the reason he promotes the Mars idea is simply to drive up his brand and attract investment attention from people who have more money than wisdom.
Trust me, if you took the time to listen to him like I have, you'd realize he's incredibly knowledgeable. He dives into details like no other CEO out there.
While achieving the dream may seem far off, I deeply admire such a bold vision. Considering we've already reached the moon, Mars is the next logical step. However, let's not interpret this too literally. Our immediate focus should be on landing on Mars; details like building a base can come later. Humanity shines brightest when reaching for seemingly impossible dreams.
"When you reach for the stars, you might not quite get one, but you won't come up with a handful of mud either."
- Leo Burnett
My favorite quote.