Unfortunately, most people don't do these calculations, so it's refreshing to see a potential company owner who is at least thinking about it! All this comes from my Operational Flying book:
Cashflow is King, so you want as few surprises as possible, so if you can find someone who will let you borrow the machine under a contract hire basis, so much the better. The other unfortunate thing is that most companies live on cashflow, which is how they can undercut everyone else, but they have to undercut further and further to guarantee getting the work, which is a diminishing prospect. It takes guts to stick to your price!
Please do not fall into the trap of thinking that all the revenue is for spending! You must allocate a portion per hour for depreciation/repair, insurance, maintenance, salaries, etc. The problem is that you can't predict the number of hours flown in order to find out what to allocate. The question of hourly cost, believe it or not, is best solved with a graph, with overheads up the left and hours across the bottom, and costs split into fixed and variable. Where all the lines meet is your minimum cost, and the big area at the top right is your potential profit (PM me for a rough diagram)
As a rule, you would need to get around 500 hours per year to make it worthwhile, probably minimum 350
Two other tips - no discounts until some flying has been done (say every tenth hour free) as they will have the cheap flying then go elsewhere, and take their credit card details first - the more a customer wants to go in a hurry, the greater must be your insistence on payment first!
hope that helps!
Phil