I don't have much linguistics background, but it seems to me one consideration is just how "pure" your language is supposed to be. Loan words are obvious pattern-breakers, but there's also loan (or fossil) *structures* as well. Much commerce, many semi-equal cultures, and migration/ colonization could throw all sorts of modifiers in. If your subject culture is dominant or particularly prideful, they might tend to more pure forms. <shrug> ... use the language pattern for consistency, but don't get too wrapped around the axle.

Subconscious patterning might be OK. But when I do that, trying to mimic a given Earthly language, and I then look at a real map or text, there's all sorts of constructs I never would have thought of, yet which mesh perfectly.