1) How much capital do you have?
2) Are you familiar with CFR 14 Part 135 and all it's requirements?
3) What kind of maintenance schedule are you considering?
4) Where are you starting up?
5) What mission (routes) are you looking to fly?
6) What airframe will you use?
7) What does the local FSDO think of the idea, and do you have some political backing for it?
8) What kind of market share are you looking at?
9) How much planning and research have you done so far?
There's a ton of information you have left out. These are just questions that came to mind in a few seconds, and there are tons more that need answered. I watched a charter company start while I was in Newport, RI. I started CFI'ing up there in March 2003. The people were supposed to start in Spring of 2003, had been in contact with the FSDO, had political backing, money, etc. When I left in September of 2004, they still had not started flying. They are now up and running and doing some flying, but it took members of Congress and other political influences to finally get approval for it all.
You know the old saying I am sure..."How do you make a small fortune in aviation? Start with a large fortune." If you are serious, I can put you in contact with the people in RI, and I can try to answer some questions, as I was there every day during the process, but I am definitely not an expert.
Feel free to PM me if you have specific questions or want more info. It definitely takes more cojones and money than I have or am willing to risk to do what you are asking about. The example is a severe example of what could happen, and I have heard some positive and a ton more negative stories than that one. I am not trying to discourage you, but just showing you what you are getting in to. I wish you the best of luck.
TX