Let's say that I want to invent a sound which, if it already isn't a Dutch word, could potentially be one, because it exhibits the right morphology.
Is there some document where I could find "Dutch" under D in the index, and then navigate to a page starting on which all the rules are there? As in, Dutch has these phonemes, and then these rules for combining them, and so forth.
It seems that the term you are looking for is phonotactics and it has more to do with phonology than with morphology. Basically, the phonotactics of a language defines what sequences of sounds are allowed (or not allowed) and the basic syllable structure. For example, in Dutch the syllable structure is (C)(C)(C)V(C)(C)(C)(C), where C stands for consonant and V, for vowel. Letters in parentheses indicate optional sounds. Having the basic rules, you can, in theory, derive the words (even those that don't actually exist in the language).
After a quick search, I could find a small section on Wikipedia about Dutch phonotactics, which, granted, is very superficial. But I bet that if you try more academic sources, you will find more detailed information.
World phonotactics database: http://phonotactics.anu.edu.au/index.php
World Atlas of Language Structures Online: http://wals.info/
Not sure if that has morphological information or not.
