1) Interjection
"Hooray!" and others such as "Yes!" "Wow!" or "Whoa!" are all interjections. Think about them as words that interject to show an emotional response.
2) Preposition
I'm not sure how to explain it to you more in depth except I've memorized all of the prepositions and "over" is one of them.
3) Predicate Adjective
"Delicious" is describing the "smell" which is the indirect object of the direct object, "sausages."
4) Prepositional Phrase
"Before" is a preposition and anything following that preposition to a subject, which in our case would be "sunset," is a prepositional phrase.