small pole barn advice

I used to work at a concrete plant during my late teens/late twenties and saw my fair share of job sites and contractors.
That being said, we would always recommend that if the ground was disturbed, it would be prepared with a compacted base of at least 6'' of 3/4'' minus crush gravel as a base and 3/8'' by 12" in a grid rebar for a shop floor minimum. I wouldn't use mesh unless it was for a sidewalk personally.
Get the highest strength concrete you can afford with a 4 to 6 inch slump.
Don't allow them to soup it up (add extra water) so it flows easier and is easier to move.
The fiber in the concrete works well too, we did it a few times, but not often.
It was mostly used in government work for bridges of some people that had heavy duty machinery moved on it. (Read D8 Cats and the sort in a shop).
I think it's overkill in your case.
And most of all, order enough to do the job completely, you don't want to fill in some areas with rocks to make up the shortfall, or have them batch half of a yard and have extra delivery fees added!
Yes, i've seen it all!