It is a sweet bread. I wouldn't cut back too much. Try two cups. With all the other ingredients it shouldn't be too much.
Yeah it turned out fine, I used 1c brown sugar and 1 1/3c white. Didn't come out as sweet as I thought it would.
The sweet potato was less sweet than I'd expected. By the way, the food mill worked awesomely for that: chopped up and boiled the potatoes with skins, then ran them through the food mill on the medium sieve and it took the skins out and passed potato puree through. Once in a while had to crank backwards (scrapes the sieve clear), push the stuff down into the blade with a spoon, crank forward. It's dump and turn, but it's not a huge ordeal.
The food mill seems like it would be more convenient if I was making a friggin' ton of mashed potatoes. Just keep feeding it boiled potatoes, and occasionally crank back and remove all the skins to keep it clear. In small batches, things stick to the side and then you can just add more stuff and not worry about it... but you've added all two cups of food, and half of it's stuck to the side, and you need to push it down with a spoon. Ten cups of food, just keep adding and worry about the last of it when you're nearly done.
Besides pumpkin or sweet potato paste sticking to things (what did you expect...), it's an awesome kitchen tool.