Using a shotblaster is certainly the best way to prep a floor for application of an epoxy coating. I do floors for a living and we shotblast all floors. A couple of things to look out for if you do use a shotblaster.
1. Make sure you don't stand still as they will dig a hole in the concrete.
2. It will uncover cracks, we use a diamond blade to widen so filler can fit in.
3. depending on the finish that you want when done the shotblasted concrete can leave it looking rough if you do not use a 100% solids material. We do 3 coats of epoxy and then a urethane to protect further.
4. Primer should go down as the slab is cooling so it will not produce bubles int he finish. once sealed other coats can go on as needed.
5. shotblating will cause you to use more epoxy as it leaves lots of peaks and valleys to fill which is what you want. Justmake surey ou have enough material to complete the job.
IF anyone has questions I would be happy to help if I can.
Don
www.ultimategarageworks.com