1. You shouldn't have too much hand luggage. Correct
2. People who want to smoke have to sit separately.
3. You
don't have to wear your seat belt all the time. You can take it off.
4. But you HAVE TO wear it
for take-offs and landings.
Correct5. When you've got your luggage, you HAVE TO go through Customs.
Correct
We use have to when something is an obligation, it is necessary to be done.
We use should when:
Giving suggestions or advice: You should brush your teeth every day.
or to indicate probability: If I should be late, go to the cinema without me.