Hey, I've lived in West (by God) Virginia too.

When you first fire up the pump, try whacking the motor with the butt end of a 2X4 or hammer (hard enough to get it's attention, but not so hard you dent the casing) - if it's a rusted connection on the start capacitor, the motor will fire up.

As for the crete, the 3500 PSI (A/K/A 'driveway mix') is fine for a pool deck. I would go with rebar and '6X6X6' wire for reinforcement over the fibers. As for the slump, I'd have them bring it at 5 and only add water if it seems too thick for you to lay down and finish in a timely manner (you don't want to be 1/2 way through the pour and have to add more water, every time you add more water to premix, you weaken it. Also, you'd end up with disparate crete, which will weaken the final product!)

Expansion joints may or may not be necessary around the steps, but I would opt for them.

One other thing, most readymix companies charge extra for just 3 yards, it might be worth it to expand the deck in one area, so that you have a place for deck chairs, etc. - you'll not regret a larger deck in the future.

Will you have expansion joints or just control joints in the deck?

Also, it'd be nice to see some before and after pics.