It would stay molten for millions of years.

Not sure if Europa's water would be flung into space, make atmosphere, or make a boiling ocean.

There's probably a way to engineer it such that the spin of the planet is 24h, the core is spun up. We'd also like ~365 day years.

At some point I saw a design for a machine you could park at the Lagrange point between Mars and the Sun that would collect solar power and spit out a magnetic field strong enough to deflect enough of the solar winds that we wouldn't need to worry about that.

Also nobody remembers when there is nobody alive

It doesn't have to be near the sun to have heat or be warmed by the Sun. It is still currently in the goldilocks zone, same with Venus. The difference is how well each planet traps heat. No atmosphere no heat for mars, highest peak surface temperature is 70 fehrenheit or 20 celsius. Not much but enough green house gas and you could raise it by 20 degrees or more. Other thing to consider is that you don't need to move Mars, you could create artificial magnetospheres.