Here's the recipe for sweet potatoes that I think is essentially how I remember them from all of my childhood Thanksgivings. And I should know, since I ate the vast majority of them...
I can't tell you exactly how many to get - I had around 5 pounds (the store was having a 5#/$1 special on sweet potatoes, which was great.), but I increased the amount of sugar sauce later on.
Chop the potatoes into 1-2 inch chunks - you want them to be big enough that it's not too time consuming to skin them later, but at the same time they need to cook pretty quickly. Put them in a big pot, cover with water, then boil the potatoes until a fork goes into them easily. Drain the potatoes, then let them cool.
Once cool, use a dull knife to help slip off the skins of the potatoes - it should be easy, and you really shouldn't have to use much force. I recommend putting the skinned potato chunks back into the same pot.
Melt 1 stick butter in a small sauce pan, then add 1/2 cup brown sugar. You're basically just making sure they're pretty well combined. Once it has become pretty well mixed, pour it over the potato chunks, and stir thoroughly.
Pour the potatoes into a pan for baking (I used a cast iron skillet, which was almost better than a baking pan), and bake at 350 for about 30 minutes. Since everything's full cooked, you could take them out at any point really, but I feel like the longer they're in, the tastier they get. Just make sure they don't burn.