6 to 9 piece garden? Polyps?! Lol
How much room will they have? Inches?
Also they will overgrow each other no matter what you pick, your best bet would be to put little pieces of ruble or little walls or epoxy that you can easy cut the zoas mats and frag out and spread the wealth with fellow reefers.
I've seen some amazing gardens! Can't wait to see yours as well!