Legal Question in Intellectual Property in New York

The first thing I will say is that I wish you the best of luck with your new venture. The second thing I would say is to study well established film and tv review blogs and sites to get a sense of just how much (or how little) they sample for their reporting. Secondly, learn the various factors that comprise the fair use test. Bear in mind that your second assumption is correct (the actual law and application of the doctrine is vague), but also bear in mind that your first assumption is likely incorrect ("all of these things are covered under fair use"). While fair use often can be colorably asserted, you must uderstand it is a "defense" to an already valid copyright (which most movies and attendant promotional materials are in possession of). There is no automatic fair use doctrine exemption. Hence with all snippets you choose to use, you have to tolerate a certain amount of risk that a cease and desist letter might be forthcoming. However, the more hobbyist your site is (i.e., the less a clear revenue stream is being generated), the less likely the powers that be will knock on your door and the more valid your fair use defense will be.

I hope that helps and should you need legal counsel down the road, please do not hesitate to contact my office.