In days gone by I probably would have looked at something pointy, fast & exciting - like an old Hunter.
These days I'd probably be sensible and look for something I could use myself and also make some money out of by chartering - say a King Air. I'm guessing £2mil would do the job.
I'm not sure on the current price of a decent Spitfire, but one of those and trying to make it pay for itself would be a challenge. What do they go for these days, say a £mil - add another for contingencies and what not and that's £2mil
And a heli would be handy - say an AW109 - so prob another £2mil
So that's about £6mil on aircraft. There's an estate I quite like the look of for sale near me - about £6mil should sort that.
The remaining 8mil would get invested for the kids and family.
If any of the aircraft failed to pay for themselves, they'd be sold - it's entirely possible If the Spit didn't make the cut that I could have as much fun with a racing e-type jag and a Tiger Moth! I may also be tempted by a STOL type such as a Maule. Nice problem to have whichever way you look at it.