It's a big work to tackle! But the rewards are lovely. I think my personal approach would be to read through the work, identify the variations that seem the most difficult, and start with whatever number of those seem suitable to work on concurrently. Could be one variation at a time, could be more. Then I would work my way "backwards" to the technically easiest ones while continuing to polish the hard ones once the groundwork has been laid. That way, you'll be "finishing" more variations at the same time.
Topic: How should I learn the goldberg variations