Hi - i bought 10 Thuja Green Giant Arborvitae and they came bare root about 1 foot high. They seems flimsy, and wondering if worth planting right in ground (see pic), or best to leave in a pot for a year. I'd hate to give them a year of trying to grow with little progress and not make it. Otherwise, i may just buck up and buy larger ones (like 4 footers) and save these little ones for later.

Thuja Green Giant will grow fast! So as long as you can keep it happy, bigger ones are only going to be more expensive. (And all of these planting considerations will still apply.) I'd say, that as long as you can keep it watered during the drought periods while it establishes, you'd be fine planting your smaller ones now. Keeping it in a pot through the season and planting it in the fall (the other best planting time), runs the risk of underwatering the pot during the summer. So I say pick which one is likely to work best for you.