One gallon would be fine.

If it would be my cutting I would use a smaller container especially if a fast draining soil is not available. Choosing a pot that is too big will leave it wet for too long and root will rot

Repot it right at the root crown level, not deep, you don't want the trunk to rot.

I had a bad experience planting my rooted cutting deep and it rotted the stem.

Per Johns advice YEARS AGO, I planted my cutting and air layers deeper then normal, and roots have grown all the way up the stalk to the base of the soil. I did use a 5-2-1 mix and let it dry in between waterings to a lightly moist state.