I must say that I got slightely confused though when you write that obtaining a contract up front prior to acquiring an aircraft is key, along with the marketing before the helos arrive. How can you possibly seriously advertise your company when the hangar is empty?
My intention was to stress that it is important (essential?) to have work lined up before you purchase a machine, even (as mentioned) if it is only joyflights at Country Shows. A contract for an aircraft would be the ideal, but whatever it is, make sure you have a cash flow lined up before you start.
As a comparison, would you set up a coffee shop without first checking that a market exists at that location? Similar scenario: an assurance of income is essential to any new business. Along the same lines, marketing the new coffee shop prior to opening gives a better chance of getting clients than sitting behind the counter, hoping....!
Marketing means making sure Yellow Pages advert is booked before the yearly closing date, getting online coverage with Google hits, mail out to prospective clients, etc etc. If you have been operating as a pilot, use the contacts that you have built up over the years to bring some work into your company. You can only sell what you have, so choose the helicopter to suit your planned market; an R44 would better suit joyflights than a turbine (eg B206) but a 206/EC120 would better suit general charter, photography, filming etc. Costs and charter rate would reflect the income and expenses commensurate with the helicopter type and operation.