Keep in mind if you don't do the the single pilot certificate and you will need a chief pilot, DO and Director of Maintenance. This could be a huge cost if you don't have friends to help you out with this. If you start a Basic 135 Certificate, you can get a waiver to combine the DO and Chief Pilot Position and I believe the Dir of Maintenance as long as they are qualified. I would stay away from sub contractors, the paper work is not that bad as long as you follow the FAA guidance for it. An added benefit is that you will learn a lot by writing the manuals yourself.
Conklin De Decker is a great source of information for the variable and fixed costs of an aircraft
Conklin & de Decker - Aircraft Operating Costs & Aviation Services
Getting an airplane that you can instruct and charter with is a great idea as it will offset your fixed costs when the charter is slow, which it will be at times.
Pm if you wish with questions you may have. I re certified our company when I was 23 and believe me whether it works out or not it is a great learning and educational experience that you can't buy or get in Grad School and it will open up a lot of opportunities that you may have not otherwise been able to get.
PS: Before going to the FAA and doing the letter of Intent. Read through the 8900.10 Manual pertaining to Air Operator certification as this is the same thing that your POI will be using. Earn your POI's respect by doing your research and I have found that they become a lot easier to deal with.
Best of Luck,
John V