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?