Flying 5m from the water at 550km/h seems like it would be a hazard to shipping.
Being a hazard to shipping appears to be the purpose of it.
I will also say that at 5m from surface, good luck "seeing" it with on a radar. Also, at night and/or with mist.. you don't even see it coming.
If by boats you mean warships, then yes, they may cause a blip in a proper radar.
That said, at longer distances or rough seas things significantly degrade unless you’re talking about a big boat.
Normal aircraft typically spend long periods in autopilot, whereas these things would presumably require a constantly vigilant pilot. And not just to avoid big ships, there are plenty of things floating in the ocean that could destroy one of these things: small boats, buoys, debris. The mast of a small sailing dinghy would be enough to cause a catastrophic crash.
I like the idea of this kind of craft, but I can't see it working at scale.
You might be able to get it airborne without as much boost if you had the help of an intermediate phase of acceleration as a hydrofoil. The Orylonok uses a ski in this vein.
Yes, at the cost of forward speed. It would be similar to a parabolic climb in an aircraft.
As for the Kamov helicopters, no idea, but apparently coaxial rotors are more efficient (e.g. better climb rate) than the traditional helicopter design. The "next generation" Sikorsky–Boeing SB-1 also uses coaxial rotors:
https://en.wikipedia.org/wiki/Sikorsky%E2%80%93Boeing_SB-1_D...
If you start steering 30 seconds after detecting an object you would still be 5+ km away, so assuming a ship is at most 200m long you would only need a 3 degree course change to miss it by more than a ships length. Maybe make it 5 degrees to miss it by 400+ meters.