Think of when you have a bunch of batteries hooked up in parallel. Same voltage, yet less drain and stress on the batteries.
With a pressure tank you may retain a more constant pressure without constantly running your pump. Just like your pump and tank for the house, it should have it's cutoffs, regulators and such. Since you mentioned garden hose, I don't think you're irrigating Villa Olivia Golf Course or the south forty acres. Yet still, you seem to suggest a separate well for sprinkling. As a kid in Wisconsin, one pressure tank handled feeder pigs, cattle, household, and evening garden sprinkling very well. Albeit, the well probably took up most of the electric bill out of anything else..
Now as to the difference between a pressure tank and a sprinkler tank, I can only suspect that while they are in the same church, they occupy different pews. I'll leave that to the full time bishops that be. If there's too much pressure coming out of the hose, just turn it down a tad. Do we really need a Northstar V-8 on the Hoover Vacuum?
Hang tight for more input here and by all means feel free to clarify anything that may help us help you. If I don't see a couple of hits by Wednesday regarding my air dam on a commercial ejection pit, I'll have pictures by then as I have a habit of complicating things too.