Quick question regarding the disclosure of objectives.

Do I reveal the method of victory?

For example, as the Imperials, do I tell the rebels that for the mission entitled "Aftermath," they can win by destroying all terminals?

Are the rebels left to figure out that they need to destroy the terminals themselves?

Rules as written say you read everything to the rebels in the mission briefing. You only read events as they're triggered, but once they do, you read that to the rebels as well. What you don't read is the options you don't take in an either or situation. So if it says you can lock a door or deploy a nexu, only read the option you took.

However certain rules can be house ruled by group vote, for example we tried playing where we didn't know turn limits. The imperial player would hint by saying 'you need to move quickly', or something.

But the rebels need to know what their objectives are.

Read the second page of the campaign book. Read it also aloud to the rebel players, or let them read it themselves. There is nothing secret in the campaign book before page 4.

Yes, you read each event as it happens, not before, including the mission briefing. You read both the flavor text and the associated rules block and repeat as many times and at any time the rebels want to hear them. You read everything except the options the imperial player did not choose. (I also don't indicate that the imperial player has options to choose from, but that is strictly-speaking a house rule. I also don't read any sections in the mission results that were not fulfilled.)

The rebels always know their losing condition, and usually their win condition. When they don't know their winning condition, they know how to progress the mission to get to know it.