"Using the panel as a raceway is also allowed." Very true, but a lot of people get wierd about it... Feed thrus, and wire nuts in a panel are contensious items. The longer you're in this Trade, the more opinions you'll come across. Some will make sense, some will not.
Anyway, as far as running with feeders, and through nipples it's very important to stay to the allowable derating. It could throw that plan out the window. See 310.15! But as long as you're covered there, it should be ok. Believe it or not, the best tool in your belt could be a calculator! You'll have more to think about than math....
Another word of advise.... Obtain a Handbook version of the code, it will clear up alot of vague items. It's got commentary on every third code, or so, in plain english.
