Germinated, then what?

This last fall I collected Japanese maple seed from 4 different maples cultivars. I stratified them in the fridge for several weeks and planted them in seedling trays to celebrate the new year. The good news is, now I have a great crop of new little maple seedlings. In the next month or so it should be about time to transfer them to larger pots. I would plant them in the ground and let them develop, but I'll be moving again in the fall and would then have to dig them up again.

My question is, what size pots would be appropriate for a first year seedling?

Coffee mug size.

Or you can plant them on 2-3" (5 -7.5 cm) centers in a large, shallow (2-3", 5 - 7.5 cm deep) pot or flat. I find it easier to handle the flat rather than a large number of small pots. In addition, the roots can spread more resulting in more growth and it is easier to keep the flat evenly moist, particularly on hot days.

Marty