It takes 8 weeks to build. It = the hotel
It takes 8 weeks to build it. The first it = empty subject to make the serntence grammatical.
Of the two, the first sound better to me.
Can I say "They take 8 hours to get home" or do I have to say "It takes 8 hours for them to get home". (Or It takes them 8 hours....)
You can use both, though the second form is more common.