You shouldn't NEED to ask the company for permission, as long as you make sure to respect all of their copyrights. Double check on the specifics of fair-use and such with a lawyer.
This is mainly because some companies will provide free or discounted copies of their product or possibly other info about the product for press inquiries, which your site could be considered, depending on how the company views you.
You could either write them yourself, find someone to write them for you, or do something like Amazon does and have a section for each game were members could post their own little reviews about them.
No, you are allowed to review anything as long as you don't start making up lies and other garbage to hurt their sales.
You won't be able to get anything free until you have a large site with members/visitors. I would do it, though, once you get big enough. If you start getting free games, you could find more people to do the reviewing, which would make your site bigger, and then you would get more free games!
