Thought I'd give you one more thing to keep in mind.
Before 1906 there were only two documents kept. The first was a very short Declaration of Intent, the second the Naturalization Petition. Neither one gave much information, but the DOI gave more than the NP.
After 1906, there were three documents kept. First was a lengthy Declaration of Intent. For research purposes, that's the most important document. Then came the Naturalization Petition, and that will tell you how long the person lived in the US and in the jurisdiction of the Naturalization Court where they made the application. The third was the actual Naturalization Certificate, and it's really cool to have, but not of much research value.
BTW, also found the answer to the residency question. Between 1906 and 1951, they needed to prove that they lived in the US for five years and within the jurisdiction of the Naturalization Court for 3 months. Hope that helps.