1. At nine, the buses will depart for Lorca Beach.

2. At nine, the buses will leave for Lorca Beach.

3. At nine, the buses will set out for Lorca Beach.

4. At nine, the buses will start for Lorca Beach.

5. At nine, the buses will ____ ____ Lorca Beach.

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Can we use all the expressions? Do you have some more similar expressions for #5?

Yes, all are appropriate. "To depart" seems a little formal, but it's perfectly appropriate. I can't think of another way to say it, but there may be others.