A good post.
You will get a multitude of replies obviously and with wildly countering points of view.
I do get involved in buying and selling a bit, - both for myself and doing pre-purchase reports for others.
A few things caught my eye. For starters you sound like a typical first time owner operator.... that has to be a good thing.
You are not seeking or expecting anything out of the ordinary.
Your envisaged utilisation will be optimistic. It always is. If you can get up to that figure it will make your operating costs look a lot more realistic.
There will be a big difference in the cost of operating a retractable over a fixed gear machine. Your flights are not that long and few and far between.. you may want to broaden the range a little as a result.
You will also discover that there is a big difference in operating costs between manufacturers.
Brand C engines may cost more to operate than brand L for example.
Similarly brand C aircraft may be more than brand P..... I say maybe because you will never get agreement there.
I have been around long enough to know the maintenance requirements of most of those machine. Recently I spoke to other Chief Engineers and we were all thinking along the same lines.
The best thing for you is to do your research. Keep an open mind, - but then get a good and knowledgeable character to do the pre-purchase.
You can never ask too many questions.
All the best with it, I believe it is a buyers market.