jxc
I believe Amy Johnson had less than 150 hours when she set off on her Australia flight.
This was in a tiny Gypsy Moth with only a basic turn & slip for blind flying and a cruise speed of 80 mph.
So, I say, ignore the doom and gloom jeremiahs and go for it. If you fail, then at least you will have had the satisfaction of having tried an endeavour which not many of us would even contemplate.
Good luck to you and your son and I hope you raise a lot of money for a good cause.
Dak