No response yet, so I figure it's as nice out where you are as here.

I'm thinking this could be a good back-up for power outage and I'm looking for 'inexpensive' ways of getting more water.

Yes, I know, these tanks are not cheap.

Just curious what you all have done and what you've learned.

"Just read an article talking about the benefits of adding multiple pressure tanks to the system. "

More tanks equal greater drawdown volume, true. But a larger tank won't have synchronization problems that multiples could, which will INCREASE pump cycling and take up more space to boot.

"I'm thinking this could be a good back-up for power outage..."

Not in the sense of having reserve water. You're better off filling jugs and storing in advance.

When my well contractor replaced my pump with a higher GPM one (after a drawdown test showed the well could supply it), he also had to increase the pressure tank volume, so the new pump wouldn't cycle too frequently. He accomplished this by adding a second pressure tank, in parallel with the original one. They're of similar if not identical size.