Calculating the TCO is not that easy done, as you have to decide how to treat certain things in calculation. For example, you could build surplus funds for OH every month, or you depreciate and distribute the purchase price over a certain period. In first case you have the funds saved when OH comes, in second case a plane with book value zero.
Comparing charter with own plane is also not that easy, as it is not 1:1 match. A charter plane is operated commercially with no on condition parts, a thing you most probably will do when operating your own plane. Assume cost savings is not the big issue for an own plane, longterm cost differences are not that tremendous.
The big decision is: do you WANT your own plane? This is feeling and weighting the balance between always availability and labor to spend as well. If you are willing to spent hours caring for the plane, buy one. If you are bored from caring, don't.
From calculation the crucial point is how many hours a years are you going to fly? If you do 50h I wouldn't recommend, 100h is fine, more an own plane plays it's availability card.
I was wondering about the total costs and started with an excel sheet since I bought my current plane.