G'day Chris,
First of all - there's a LOT of information out there about setting up and managing a business and the key to having it successfully run is to research, research, research!
Secondly, all of this depends on where you are.
In Australia, for instance, it's as simple as registering a business name and a business number. Here we have different types of businesses, however; corporations, registered businesses, sole traders etc. The US, for instance, has a distinction between an LLC and other types of businesses. The type of structure you choose will directly affect how your business operates! For instance, a sole trade in Oz means you pay for everything and make all the money... but what happens if you get sued? Well, the lawyers can get their hands on your personal assets in addition to any money you may owe... Limited Liabilites are exactly what they sound like - designed to help limit the liability and to have a clear separation between business and personal.
I won't really comment too much on the actor's contracts. At a minimum, you need a release form. Some areas dictate a minimum payment amount (for instance, I believe in Melbourne there are cases where the minimum is about $100/day and the government dictates this) so you can't just pay them $1 a call it a day. Then you have to worry about dealing with talent who are a part of the union etc. etc. It's very very murky.
Word to the wise: most serious actors won't take just a percentage of the movie proceeds. Blame this on the shady studios who screw over their staff with dodgy accounting. If a casting agent for a movie approached me with an offer like that it shows:
1.) They don't respect me enough to pay me. I'm working, why shouldn't I be making money?
2.) They don't have a large backing or don't have a strong investment in this production.
Personally I would instantly add that agent to my Do Not Call list...
The over-riding important thing is to figure out if what you want to do is going to be viable. I don't really have any idea about what it is that you plan to do... BUT, case in point; I did a marketing launch for a group of guys who wanted to make a T-Shirt company (real original idea... NOT!) I met the entire team. They had 2 artists, with one of the artists doubling as the group leader and 4 other guys who sat around and did nothing... They had no plan for how to divide the profits or how to invest.. There was one guy in particular who never showed up and never did anything, but was a friend of the lead artist who, I guess, must've felt inclined to have this guy on board. I personally think this is a very BADLY designed business which will only be profitable with a god-given miracle.
So my advice is to sit down and work out exactly what you want to do, and talk about the hard questions straight away; if someone walks in with $10 million and wants to give it to you for free, do you guys split it 50/50? How much do you reinvest into the business? Do you have a "buy-out" amount (i.e: you get sick of doing the business, so your partner pays you $X for your stake in the business).
Phew, I could write forever. Anyway, there's a reason making and managing a business is hard - if it wasn't, everyone would be doing it and nobody would buy anything, haha.