Noise reduction, especially in Europe, I don't know about... But I would think it's a pretty safe assumption that anything you were to buy that's relatively new would meet the European noise requirements because, well, they like to sell airplanes. Now, something like an old Lear that needs a "hush kit" is different... But I wouldn't worry about that too much, because you probably want something relatively new.
500 hours with IR and complex is probably the bare minimum, and you're going to need a lot of training and probably a mentor pilot for a while. You would probably want that on the first few crossings anyway. But, if you have enough money, it's probably do-able.
On the small end, a Cessna Citation M2, Embraer Phenom 100, or HondaJet runs about $4.5 mil, while $9.5 mil will get you into the top end of the single-pilot jets (CJ4, PC24, Phenom 300) but then you wouldn't have any money left over to actually fly the darn thing... And they take plenty of money. According the Internet, even an M2 will run about $1300/hr.
Looking at the trip: KEWN direct to EGLC (London City airport) is 3,352 nm, far beyond the range of the M2/Phenom 100 plus you won't be getting direct anyway. You'll need at least three legs with this class of aircraft, and you'll only be able to take a couple of people with you with full fuel (slightly under 600lb payload with full fuel).
But, what you also need to consider with the jet is not just its total range, which is based on cruising up high where jets are the most efficient, but also what happens in one of two situations: First, and engine failure, which will leave you without enough power to maintain altitude, and second, a pressurization failure, which will also necessitate a lower altitude. Those low altitudes will cause you to burn more fuel, which will shrink your range.
Now, it's "only" 9.5 mil - This isn't Powerball money. The used market offers some nice options.
For example,
this Phenom 100E for $2.7 mil. It looks like, to do this trip safely with the above caveats in mind, you'll need to make this a four-leg trip, adding Narsarsauq, Greenland to ensure that you'll be able to make it to land in the event of an engine out or pressurization emergency: KEWN-CYYR-BGBW-BIKF-EGLC. On the way back, EGLC-EGPL-BIKF-BGBW-CYYR-KEWN (plus one stop to clear customs). And this is really a two-day trip in each direction, because flight time will be around 12 hours, then you add stops and that's really too long of a day to do safely as a single pilot. But, you might want to have some fun exploring the stopover cities.
This will also give you the most leftover money for your retirement and operating costs.
Another option would be to go with a used longer-range single-pilot jet, like
this $5.8 mil Citation CJ4 or
this $6.6 mil Citation CJ3+. You can probably kiss the retirement goodbye, but you'll be able to take your 5 pax, with a full fuel payload double that of the smaller jets above (1200ish pounds) and still have some money left over for operating costs. You'll only need three legs (KEWN-CYYR-BIKF-EGLC) and flight time will be about 10 hours. So, maybe possible in a day, though I still wouldn't recommend it. If you wake up at 6 AM EST and depart at 8 AM EST, keep each stop to an hour, you'll arrive in London at 1 AM GMT anyway.
Finally, you could forego the single-pilot option, hire that mentor pilot you're going to want for some stuff anyway, and get
this $4.7 mil Citation X. You could theoretically make the trip direct in under 7 hours with today's weather, though that would give you some "feet wet" time in the case of an emergency. However, a single stopover at Gander gives you the ability to make the trip with a single stop in a single day and take all your friends.
Finally, you could theoretically lease back any of the above and help earn back your retirement. Y'know, as long as we're fantasizing.
