Mad mission: Trans-atlantic

No, no, and no.

Neither the 52 or 66 or the 86 is a trans-Atlantic boat. That's if they had the range, which they don't.

Add to that you're not in any way qualified or experienced enough to cross the Atlantic alone. I don't believe anyone should attempt to cross alone even in a capable boat as, in my opinion, you're not capable of maintaining watch at all times and that is important. Do you understand how many days are required to cross at 10-12 knots?

Now as to the boats you mentioned, the 52' is a great one person boat and the Manhattan 52 I think is one of the best new designs I've seen. As to the Manhattan 66, we did the loop in the Manhattan 65 and loved it, but one reason we sold it was that we like the 66 better. However, while many get the 66 with plans of owner operation, that means two people and cruising on it with no crew would be very tiring. I would think you'd end up feeling more like crew than owner. While it's easy to operate any of these and one person could even take a trip on the 86, it's definitely not what I see for owner/operator if cruising it heavily and I think needs a crew.

You're looking to fulfill two mutually exclusive desires. If you want a boat that can easily be single handed and that is capable of crossing the Atlantic, you're looking at a KK or something similar. Even then I don't believe in single operating on a long trip requiring sleep.

A motor yacht <60 is not going to make it, even with a good current.
Look at what the seasoned people are doing, sailing and averaging 4 to 6 kts on a rare good crossing.
Stay in the med with the MY, You want to cross, get into LSD; Long range, Slow speed, Displacement.
By the time you arrive anywhere, you will be even more nuts. At that speed, it takes a rotating crew for watch cycles.

Soon, these single hand sailors that get in trouble will be asked who and how watch was kept. Demanding watch records.
Of course they will fail that question and cost & fines will start coming down on them for rescues.

Well if you try to go up the West Coast to get to NY, you're going to have a very long trip.
If you're very careful about weather windows and willing to wait a lot, a 52' can get you a lot of the places you mention. However, for the trip to LA and cruising the Caribbean, I'd go for the 66'. Use a captain until you learn. Then if you want, use a mate or deckhand. Or at least plan on paying to get the boat washed and wiped down when arriving. Otherwise you'll spend your days working instead of enjoying. Now, I don't know your mechanical capabilities at all. If you're not knowledgeable, that may be your longer learning curve for single handling.
As to smaller boats that can cross oceans, KK, Fleming, Nordhavn, Outer Reef, and Defever are among some that have done so. Personally, I'm not bold enough to cross in any boat under 80' but I know people who have crossed in KK42's and many in Nordhavn 62's. Mostly it takes a displacement hull and most have a small single engine with perhaps a wing engine. But let's say you love a Nordhavn 6. Now, do you want to be limited to 6-8 knots when cruising at home and do you want to live with a 6'8" draft which eliminates the Loop and makes timing tides essential on the ICW.
As to small semi-displacement and planning hulls, in typical ocean crossing conditions they'd make you so sick or miserable you'd have a "For Sale" sign on them before you arrived, although a bit foolish to even discuss with their lack of range. Any of the smaller boats will handle a lot worse conditions than you can. A 66' Sunseeker can handle 10-12' seas but I don't know anyone who would like to be on one for more than a very short time in such seas. Crossing the Atlantic you could hit 20' seas or even 30' or greater. Unlikely, but highly likely you'll see some days with seas over 10'. In those boats, even 72 hours consecutive at 6-8' with short periods with 25 knot winds would be miserable.
The majority of people who cross oceans do so on sailboats. Most ship their powerboat across.

There's a guy on M/Y Dauntless, a Kadey Krogen 42, who has crossed the Atlantic going east, solo, and then crossed back, did the canal and is now going up the west coast to Alaska and then on to Japan. A lot of it solo and some parts with one crew.
Can be done, not by me though.

The 66 vs. 52. Most on a 66 need a second hand for docking and locking where one person can easier do the 52. Washdowns, waxing, all cleaning tasks are probably 60-70% more work, not the 33% you'd think if all you considered was length. You have beam and height influence.

Your lack of experience would mean quite a while before you could manage either solo, but longer for the 66. I know experienced captains who will not move a 66 without a second hand. Yet, some owners are comfortable doing so.

Now, let's talk rough water. Again, the 66 is 60-70% more boat. The 52' weighs 59,000 lbs., the 66' weighs 82,000 lbs. The 66 will handle rough conditions better than the 52.

You will see boats equal to the 52 in the Panama Canal. None of this is saying they can't do it. However, it's really a moot argument as you cannot get beyond the fuel shortage and range limitations of the 52. You'd have to carry 500 gallons of fuel in bladders. That's a lot of bulk and 3500 lbs. They would have to be mounted to they could withstand rough water and wouldn't move around.

Some things give you an indication of what kind of cruising the manufacturer thought the boat was appropriate for. With the 52', the fuel tells you "short cruises".

Yes, there is a significant cost difference both new and in operating. If your desire is to cruise the world though neither of these is right. If it's to cruise the US and Bahamas, then either can work.

There is a boat company that specializes in long-range powerboats called Nordhavn. Many Nordhavn owners have taken their boats across the Atlantic or in some cases around the world. I believe the company web site may include links to Nordhavn owner blogs about their ocean passages. Several Nordhavn owners run their boats without crew up to 60' long.

If you have to come here to ask the questions.... the answer is "hell no". Crossings are to recreational boating what Everest is to hiking. Only after you spend a lot of time practicing and learning the skills on easier terrain, and understanding the equipment can you, for yourself, answer the question.

I started messing on the water 58 years ago. I have not crossed on the water, (about 1500 crossings in the air, but that's different) but I have thousands of miles under my belt on open water, much of it solo, all of it on sail boats pretty well equipped, and operated with due caution. I can talk about what kind of boat and equipment would work in that environment.

I have not played with power boats enough to have the same discussion there. But, from what I can see there are very few boats that are not large that I would take too far out on the lake. The Nordhavn mentioned above seems to be one of them. They are not cheap.

Go out and learn..... Keep your stated goal in mind and decide when, if ever, you have the skills and the knowledge to do so.

Oh, the "no one should be out there alone, watch schedules etc etc" is blah blah. There are plenty of solo mariners that are quite capable of operating safely. There are plenty of crews that shouldn't be allowed to leave the dock.