Pothos is a very easy to grow plant that is forgiving of many growing conditions.
Choose a pot that comfortably fits the root system with an inch of so of new grow space around the root ball.
Do not go to large of a pot size as this can lead to overwatering.
Make sure the pot has a good drainage hole and use a good quality potting soil.
As long as you pothos looks good, there's no need to worry about whether the roots are crowded or spread out. I've seen root-bound pothos doing just as well as those with their roots spread out. Pothos is an extremely common and popular houseplant because it accepts growing in a wide variety of conditions.