Learn Italian: Il progetto inizia ufficialmente domani. - The project officially begins tomorrow.

The adverb is formed from the adjective ufficiale. Normally, you add -mente to the feminine singular form of an adjective. However, there's a specific rule for adjectives ending in -le or -re (like ufficiale, facile, or particolare): you must drop the final -e before adding -mente. So, it becomes ufficialmente, rather than ufficialemente.

Could I use the future tense inizierà since the sentence is talking about domani?

Yes, inizierà is completely grammatically correct. However, just like in English ("The project begins tomorrow"), Italian often uses the present indicative tense for scheduled, certain future events. Using the present tense inizia here makes the start date sound like a firmly established, unchangeable fact.

Why is the adverb ufficialmente placed between the verb and the time word domani?

In Italian, adverbs of manner (how something happens) usually go directly after the conjugated verb they modify. Time adverbs like domani tend to be more flexible and often go at the end of the sentence or clause. Therefore, inizia ufficialmente domani sounds much more natural than putting ufficialmente at the very end.

Inizia is used on its own here, but don't I sometimes need a preposition after it?