Depends on the planning permission the site has got and its owners' policy. One site I regularly visit specifically excludes permanent living there, although people may spend 11 months of the year actually in there!

Some holiday parks will close down for a month a year (or longer), when everyone has to leave, but some others are designed as year-round holiday cottages, so you can live there as a home. Obviously, you'll have to register for council tax, etc.

That probably doesn't help you much - speak to the holiday park owner to see what they think.

Yup...depends. You'll need to pay council tax as well.

check the lease, you may only be able to stay 10-11 months a year. and TSG is right, if its your only home, you get to pay Council Tax, and if its a secoind home, guess what........got you coming and going, although it may only be half at the second home. check with the local council too.
talk to other residents, see what they say, you may not get the whole story from someone who is trying to sell you something.