It doesn't sound sufficient. I also don't see enough info. Building something like this the DIY way can be incredibly fun and rewarding, but a key first step is putting together a proper design. It sounds like you don't have building plans. You need something to guide you. For something like this, I'm sure there are plans available online that you could buy that would provide all the detail you need. Or hire someone to do the plans if you don't have the experience (my state lets you do your own plans). I also don't see how you'd get a building permit for a 2 story structure without a set of plans.
But to address your question on piers: an 80 lb bag of concrete will only be enough for a round footing 12 inches in diameter and 10 inches thick. Around here, that's not enough. Also, piers every 5 feet sounds like a really uneconomical way to build a shop type of building. But again, I don't have a lot of info to go on.
Things you need to consider for sizing the footings:
1. Frost line depth, that tells you how deep to go
2. Loads from the structure transmitted to each pier (you need to know all your loads, dead, live, wind, rain, snow, seismic, if any), to calculate the load on the soil
3. Bearing capacity of soil, to size the pier based on the load you calculated
That's my humble advice. Also post back with more info on the structure, and maybe we can help some more.