What is the verb phrase iwould have driven more if your dad would let you?
would have driven
It could be either, depending on the word modified. It would more likely be an adverb phrase (e.g. looked at the moon, aimed at the moon). But it might conceivably modify a noun as in "Our base at the moon recorded the eclipse." It would more likely be "on the moon" but it would still be a valid phrase.
Whilst in its true sense the phrase "more than happy" means ecstatic, or very very happy, in my opinion the phrase has been used more in more of a formal manner to convey a general willingness to perform a particular service or to do something. For instance, you would be less likely to use this phrase when speaking to friends or family members; "I would be more than happy to have dinner with you on…
What is the difference between a prepositional phrase that functions as an adjective phrase and one that functions as an adverb phrase?
No, the correct phrase in American English would be "There is more than one mirror." Although technically referring to a plural noun, in most contexts "more" is treated as singular which then requires a singular verb. In the question's phrase, "one" is modifying "mirrors"; since the adjective is singular, the noun would be singular as well.
How would you punctuate this sentence In addition the more severe forms of mood disorders may include psychotic features?
Whenever a sentence begins with 'if', 'because', 'when', or 'for', a comma must be used at the end of the first phrase of the sentence. In this case, the first phrase happens to be a simple two-word participial phrase and would be punctuated thusly: "In addition, the more severe forms of mood disorders may include psychotic features."