Zutano seems to be a fine rootstock. You might be able to order 100 zutano seeds in bags from brokaw for cheap. I would go with those. Clonal rootstock can be more salt tolerant(doesnt matter for you) or more root rot resistant.
I would try and contact brokaw and tell them what you are doing and what your soil and rainfall is like and see what they say.
I called Brokaw nursery today . They want like $32-$34 a tree so I doubt that four winds is getting them from them anymore because they’re offering me a 30% discount if I buy more than 120 trees. It would make each tree about 24 1/2 dollars plus shipping which would be about $28 . They also can not get Gem or Sharwil trees.
The trees from four winds are 5 x 5” and 12 inches deep and 2 to 3 feet tall . Not sure where they’re getting them from but they can’t be getting them from Brokaw. Brokaw doesn’t give discounts not matter how many you buy too. Somehow four winds is still getting a discount for over 120 trees .
Of course I will graft my own trees when I’m able to grow some Zutano seeds I do have a Zutano tree so I should be able to start doing that soon .