Yes, but only if it is not prohibited by the landowner. The landowner is within their rights to prohibit photography on their property or to require payment for permission.

If there are 'no photography' signs or terms of admission that forbid photography, you commit a trespass by taking photos, and may be told to leave. If you do not leave immediately reasonable force may be used to eject you. You may also be injuncted or sued for damages in a civil court. However the landowner or staff do not have any legal power to demand handover of film or memory cards, nor to require the deletion of images. 

You must ask the landowner, or their agent or representative. On private land open to the public permission will allow you to photograph people without their individual consent, but note that privacy considerations will still apply. You should not photograph anyone in circumstances where they might normally expect privacy without obtaining their consent.

If you take photos on private land without permission, whether photography is prohibited or not the photographs are your copyright.

There are occasions where if the landowner can demonstrate to the court that your copyright represents a financial loss, eg because he himself sells photos of his property, then the court may intervene and award economic copyright to him.

Not unless you are intending to sell the picture for advertising or marketing use. A model release is a binding contract that agrees to relinquish specific future claims of equity in return for a 'valuable consideration'. This is usually payment, but can be prints or some other agreeable exchange.