Pot size Auto

20 works best.

Yes - depends on space. Most important thing to remember is an autoflower will start to flower when the tap root hits the bottom of the pot and starts curling around. I find that 5 gallon buckets make for fairly good size autoflowers, but 5 gallon fabric pots will start to flower before the 5 gallon buckets because they are not as deep.

Either is fine and mostly just impacts frequency of irrigation for an autoflower timeframe. Soil would probably benefit from14L, but soilless would be inconsequential beyond frequency of irrigation..

That really depends on how large a space you grow in and the number of plants. The type of substrate is important too, you can get away with smaller pots with coco if you don't mind feeding more frequently.

For an auto you don’t want to end up transplanting. If you can handle the 14l then that is your best bet. It will grow bigger giving you a better yield.

not a massive difference so I would go with whatever fits in the space. In general Bigger pot = Bigger plant