Making crisp hash browns

Your dealing with a few things here. First is starches in general. The thing to know about starches is how they gelatinize and at what temperatures.

This powerpoint is a nice primer on that topic. www.cfs.purdue.edu/class/f&n630/gelatinization.ppt

Basically your dealing with amylose and amylopectin, together they are what we know as a starch. When they come in contact with water the starch cells begin to swell and when their gelatinization temperature is met they burst and release their contents into the medium they are in. In the case of a dough ball, your dealing with tons and tons of little cells being held together loosely at first by the physical pressure of kneading them into balls and then when the heat causes the starches to gelatinize they adhere to one another kind of like being caught in a net.

Now the fluffiness portion of the question can really depend on how the dough is being cooked. For something like a dumpling being cooked in the boiling water, one would typically want to work the dough as little as possible to avoid making it too dense and if using flour to lessen the gluten formation that can make it very chewy like bread. Some recipes call for leaveners that can create gas bubbles when heated to a certain temperature and then through gelatinization the bubbles are trapped inside the dough and create an airy texture.

I have used these tips from TheKitchn for my latkes and they have always turned out fantastically!

1. Strain, Squeeze, Strain: To avoid soggy latkes, you need to wring out your potato mixture really, really well. Folks have different theories about how many times you should wring out the mixture and what you should use. I favor cheesecloth if you have it. If you don't, a clean dishtowel will do the trick. Just keep in mind that you can't do this too firmly: it's impossible to hurt the latke mixture. Be tough. Be firm. Squeeze like there's no tomorrow. Then squeeze again.
2. Watch Your Oil Temperature: This is the one tip that I struggle with mainly because I don't do much frying at home. So I usually end up heating my oil too much and burning the outside of my latkes and then the insides aren't even cooked all the way through. My dad always puts a pinch of the latke mixture into the pan before frying up the latkes. If it's at medium heat and it still sizzles, the oil is ready.
3. Finesse Your Timing. Or Don't: In our family, we eat the latkes to order. So some of us will have a few while the others don't yet have one and my dad is standing cooking them off the whole time. While I generally love sitting down to eat together as a family, latke season is the one exception. After resting for a moment on a paper towel to drain, they're really best right out of the skillet. That being said, if you're serving them for a party or would rather set out a large plate for folks to serve themselves, you most certainly can set the oven to 300 F to keep cooked latkes warm while you cook off remaining ones.

Additionally, on the consistency of batter/how to handle potato prep please see here for this this is a great tip about hand grating.

Hope this helps and good luck!

(Edited to clarify final tip (thanks Laura))