Is the tense correct?

Could you please help me correct these sentences?

Should it be 'once I did it' ?
I don't think I'd be able to work 2 shifts in a row, but once I did it I'd be happy.

Which tense should I use if I want to use 'when' Does it go with would?
If you watched a movie without volume
You would think that the actors overact when you watch a movie without volume.

Thank you so much