Learn Italian: Nonostante la bufera, avevamo iniziato il montaggio. - Despite the storm, we had started the setup.

Nonostante can act as a preposition or a conjunction. When followed directly by a noun like la bufera, it acts as a preposition and doesn't need che (just like 'despite the storm' in English). You only add che when a verb follows, which would then require the subjunctive, for example: nonostante che la bufera fosse forte.

Could I use 'malgrado' instead of 'nonostante' in this sentence?

Yes, malgrado la bufera means exactly the same thing. Both nonostante and malgrado are concessive prepositions that can be used interchangeably directly before a noun to mean 'despite' or 'in spite of'.

Does 'nonostante' ever need a preposition like 'di' after it, similar to 'in spite of' in English?

No, nonostante and malgrado connect directly to the noun and its definite article. English speakers often accidentally say nonostante della bufera because they are translating 'in spite of', but in Italian, no extra preposition is used.

Why use the past perfect (avevamo iniziato) here instead of the passato prossimo (abbiamo iniziato)?

Avevamo iniziato translates to 'we had started' and shows that the setup began before another past event not explicitly mentioned here, such as before the storm got really bad. If you used abbiamo iniziato, it would simply mean 'we started' without highlighting that sequence of past events.