Laura,
From what I've seen, they don't show suckers until the main stem is about 2-3 inches in diameter and has leaves several feet long. In other words, they need to get a bit larger before you know.
Planting several together is perfectly fine and will look great whether they sucker or not.
They are good growers so if you plant a one gallon out I think you'll start getting trunk in 2 years approximately.
Here in SoCal they sunburn when young but can eventually take the full sun once established.