Pothos is no longer allowed in my tanks, same with lucky bamboo. I had such bad experience with them. They didn't do anything. I think people who say these plants worked must have had a ton of them in their tanks. Mine just rotted away or fish will chew on it.
Here's a sure fire way to remove nitrates without plants.
drain out water (I do it halfway)
then fill back up
then drain again half of what you drained before
then fill back
do it again the following week
I don't know how well they keep nitrates down but they grow like weeds if they have proper lighting.
As for the second part that's a little pointless.
Say you have 100ppm nitrates for simplicity
You do a 50% water change you now have 50ppm
Do another 50% water change with your 50ppm nitrates and you now have 25ppm
Take that same 100ppm nitrates
Do a 75% water change you now have 25ppm nitrates with less water and time consumed
Do a 90% water change and you now have 10ppm with still less water and time consumed.