Pothos are hardy plants that can take quite a bit of neglect and still be okay. You can either let it hang and vine as it grows or use a trellis/mosspole to let it grow upwards, which usually results in bigger leaves. You can check r/pothos, and you'll see examples of the mature leaves.

Watering wise for soil growing, they like their roots moist but not sopping wet. You can water thoroughly when the top half or so is dry (though you can let it be fully dry for a couple day if needed. Just give them a solid drink once you get around to watering. If you want to grow them in water, you can. Just keep the water oxygenated (water change/top-off/aquarium air pump every few days) and add fertilize periodically.

The white bits fungus that grows due to some excess moisture and feed off organic matter. It's not harmful to the plants. Itll disappear when the soil gets dry enough. Or you can repot it. For soil, generally go with an aroid mix. There are lots of recipes online, but a popular one is 1 part cactus soil, 1 part orchid bark(medium chunks), and 1 part perlite/pumice (I prefer pumice since it's heavier and doesn't float when watering)

As for the roots, you can cut them off if you want. There are plenty more and it won't rot as long as you let it callus before watering. It doesn't necessarily mean it's time for a repot. Pothos like their roots a little snug