Syntax of 'Number Number MeasureWord'
Must the numerals be monosyllables?
In my opinion, you can use multi-sllable numbers, like:

十五六公里 (fifteen or sixteen kilometers)
百八十个 (one hundred or eighty)
三十七八岁 (thirty-seven or thirty-eight years old)

Restrictions on the measure words?
No, I have no idea.
Can there be at most two numerals?
Yes, I have never seen more than 2 numbers used in such a pattern. This pattern is used to express an estimation, an approximation.