Here on garden.org, the smallest container size recommended for any variety of abutilon is 3 gallons. This surprised me a bit, given that fuchsia are labeled for 1 gallon.

What do you think is a reasonable minimum pot size dwarf abutilon with a mature size of 12"-12"? What about a container with a dwarf abutilon and a fuchsia? Is that a doable plant combo for a large hanging basket?

My garden centers sell small abutilon in the spring in 4-6" pots. I plant them in all size containers with other summer annuals. I have grown them in 10-12" hanging baskets as well, usually with other plants in the basket. They do well. I water them with dilute fertilizer periodically.