How much gravity do I need to bottle w/o backsweetening?

I'm about 11 days into fermentation on my first cider, 5 gallons of apple juice, 4 pounds dextrose, and 8.9 ounces of brown sugar.

US-04 yeast, OG was 1.080.

How many gravity points does it usually take to carb up in the bottle? I'm probably aiming to bottle right around 1.018-1.020, is that going to leave me enough sugar for the yeast to do their thing?

I last took a gravity reading two days ago, and it was at 1.028, hoping I didn't get stuck. if I do, I'll probably just need to pitch some washed slurry from an old batch of US-05. Shouldn't cause too many issues to jumpstart things again, yeah?

A standard cider carbonation uses up 0.003-0.004 gravity points. Bottling at 1.018-1.020 should end up in the 1.014-1.017 range for a final gravity resulting in a semi-sweet/sweet cider.

That's what I'm aiming for, something to please the non-beer drinkers (aka BMC ladies). Thank you!