The trick to predicting cash-flow, etc for any new venture is to be as un-emotional and, therefore, realistic as possible. The trouble with the aircraft biz is it's full of aircraft - about which we all get terribly emotional - and pilot-wannebe-owner/operators - who are notoriously good at thinking with their heart when they should be using their head.
Put together your plan then get an experienced business person with no connection to, or interest in, aviation to go through it. They'll spot the holes straight away.
As for the plan itself, it's all down to homework, homework, homework. A sympathetic bank manager helps, but at the end of the day it will all boil down to how well you know the business you're getting into; where the money will come from, and where you will spend it.
Remember: "Prudicious Pre Planning Prevents Piss Poor Performance," as my instructor used to helpfully entone as my latest navigation attempt went, er, south.
Good luck
