I don't think we know much about the proper arrangement of multiple "number nouns" like {'op} and {latlh}. I'm not sure there's a significant difference in meaning between {'op latlh...} "some amount of (additional new words)" vs. {latlh 'op...} "an additional (unspecified amount of new words)". Klingons (or at least Okrand) may have a preference, but I don't think we have enough examples to figure out what the preference is yet. Personally, I'd probably end up writing {'op latlh}, though not for any specific grammatical reason. The English word order would make {'op latlh} the first suggestion to pop into my head, and since it's grammatical I'd just use that, without considering the reversed order.

(Incidentally, does anyone know what the proper linguistics term is for "number nouns" like {'op, latlh, Hoch, pagh}, etc.?)

That said, I don't think you even need the {'op}, since {latlh} without a {-mey} can still technically be singular or plural. {latlh mu'mey chu'} can mean "one additional new word" but also "more than one additional new words", which covers the "indeterminate number" idea of {'op} well enough. (Or, come to think of it, maybe you can drop the {latlh} and keep the {'op}, since the idea of {mu'mey chu'} would probably adequately convey the idea that they're additional words.)

As with a lot of stylistic questions in Klingon, the question just comes down to whichever feels best to you.