Does the final consonant have to be preceded by one vowel?

No, the final consonant doesn't *have* to be preceded by one vowel. It can be preceded by:

* One vowel: Like in "cat", "dog", "sun".

* Two or more vowels: Like in "boy", "straw", "queen".

* A consonant: Like in "strength", "blink", "film".

It depends on the word and how it's formed.

Let me know if you have a specific example in mind!