Learn Italian: Malgrado il temporale, il generatore e il catering sono pronti. - Despite the storm, the generator and the catering are ready.

Yes, but only when it introduces a clause with a verb. In this sentence, malgrado is followed directly by a noun (il temporale), so no verb is needed. If you wanted to say 'Despite it being stormy', you would need a verb and therefore the subjunctive: malgrado ci sia un temporale.

Could I use 'nonostante' instead of 'malgrado' here?

Absolutely. Malgrado and nonostante are exact synonyms when used as concessive prepositions. You can swap them freely, so Nonostante il temporale works perfectly and means the exact same thing.

Is it common to use the English word 'catering' in Italian?

Very common! Italian adopts many English words, particularly in professional contexts like business and event planning. As a foreign loanword ending in a consonant, il catering is treated as masculine and its spelling stays exactly the same if made plural.

Why does 'pronto' take the plural form 'pronti' if both the generator and the catering are singular nouns?

Because they are joined by e (and), they form a compound subject. Two singular things make a plural subject, so the adjective must be plural. Since both nouns are masculine, the adjective takes the masculine plural ending -i. Even if one of these nouns were feminine, the masculine plural pronti would still win out.