It's the same model of plane as the existing two Air Force One planes. They will tear it down and rebuild it as Air Force One. Trump wants it because it's a flying palace and believes that he will be able to keep it as is and have his own flying palace. This is cleptocracy manifest.
I have serious doubts that this thing will actually carry a president as Air Force 1 is equipped with quite a lot of equipment that civilian aircraft do not have. Some of it is top secret
Not to mention the Type 1 crypto and ECM equipment. There is no way in hell that the US would let Trump walk away with that gear. I read that it would cost from $10 million to $100 million just to sweep the thing for surveillance and tracking devices and to validate that the software hadn't been modified. Trump just thinks that this is a gift for him that's going to stay the way it is and then be transferred to him when he leaves office.
After 2029, the plane is to be transferred to the trump library, presumably refitted back to civilian spec, air force paying all costs.
There is no way in hell that the US would let Trump walk away with that gear.
10 years ago, we might have said much the same about the former President of the USA keeping most-secret classified documents unsecured in a bathroom of their resort.