As with
ANY paint or coating project, be it home, car, or maintenance shop floor, the final product is only as good as the prep going into it. Having done several shops, and helping with many more, and investigating this as a business a few years ago, the initial price of the floor coating is long gone in the total cost of the project. I have talked to companies that had $1-3/sq ft invested total in product, and were charging upwards of $12-15/sq for final install, and this was walking into an empty building. Bear this in mind when thinking you can save a little up front and repeat the process every year or two. Also, moving out and back in is no picnic, unless you have an army to throw at it, but quality can suffer when there are too many hands in a small area.
In my opinion, there is no better primer than an old, sound, well bonded coating. If it is chipping, lifting, bubbled, etc, than these areas must be addressed for good adhesion. You will need to "knock off the shine" of the old coating with something like a floor sander. There are chemicals that do this too, like TSB and Ting, but nothing better than mechanically doing it. The bare concrete areas, like Andy said, will need chemically etched, with a mix of acid and water, and rinsed and rinsed some more, until you think you're done, then once more.
Personally I like the multi part, ZERO VOC, products. These products don't "dry", they harden. In other words, if you put a gallon of product down, when it is cured, a gallon remains. These are very installer friendly too. A product that "dries" through solvent evaporation might leave behind 40-50% of the original film thickness. These are the less expensive coatings. They are quite a bit more like gluing pipe in a small hole on a hot day.
I have some more info to share, mind if I e-mail you?