The theoretical approaches I’ve seen vary quite significantly in answer to these. The one that seems most plausible to me personally (caveat: not a scientist) is basically just a satellite in near-geostationary orbit with a big electromagnet inside - the planet doesn’t need to generate its own field if we generate one to act as a shield. Of course this approach has its own shortcomings (what happens if it breaks down, for example?).

As for happening in your lifetime… that’s doubtful I’m afraid. While rebuilding an atmosphere is relatively simple it’s not relatively quick and would most likely take a couple hundred years. And that’s just the first step in terraforming - “an atmosphere” has to be turned into “ideal atmosphere”, and then the various forms of life necessary to maintain balance need to be introduced and given time to become stable.

Of course - this is all based on current technology. When it becomes a serious consideration who knows what our technological capabilities will be and how that could speed this process up?

It’s not that it gets too close to the sun - it’s that it lacks a magnetic field to shield its atmosphere from the solar winds.

Earth’s magnetic field is generated by convection currents in its molten iron core - this is suggestive that the core of Mars has either cooled significantly, or has an incorrect elemental composition.

I’ve seen a number of different theoretical approaches to solving the magnetic field issue that are all capable of being developed by our current level of technology; I suspect there will be significantly more solutions with the level of technology we’ll be at when terraforming Mars becomes a serious consideration.

As for generating an atmosphere - that is a (relatively) straightforward process that doesn’t involve much more than towing some ice from the asteroid belt (to get water) and seeding the water with Cyanobacteria and some kind of heat source.

At our current level of technology it’s not science fiction. It’s simply not economically viable.