To get the super heavy starship structure airborne and accelerate vertically, SpaceX is considering using multiple raptor engines. Clustering together huge powerful engines such as Raptor in a starship will produce, besides gigantic thrust, huge amount of heat and sound, much higher than the Merlin engines cluster in Falcon Heavy. Will not these be self destructive? How would the launch pad handle these heat energies and ensure that they are not reflected back to the rocket? Can a floating launch pad maintain it's balance and mitigate the above mentioned issues better? What about raptor to raptor induced heat?
Every high thrust launch must necessarily address the issues of heat and sound.
A flame trench can divert the exhaust away from the vehicle, significantly reducing the impact of the heat and the sound on the vehicle and on the launch pad. This means that the launch platform needs to be elevated (the approach used at Cape Canaveral in Florida) or situated near a cliff (the approach used at the Baikonur Cosmodrome).
A launch platform that is only slightly elevated above the terrain (the height of a nine or ten story building qualifies as "slightly elevated") means that a flame trench can mitigate only some of the deleterious effects of the heat and sound that result from a launch. Because the Cape is more or less at sea level, large launch systems at the Cape tend to use a water deluge system in addition to a flame trench to further reduce the otherwise deleterious effects on the launch vehicle and the launch platform. The vast amounts of liquid water released during launch absorbs much of the residual heat and sound by turning into steam.
A sea launch would hinder rather than help. It is much easier to build a launch platform that is nine or ten stories high on land that at sea, it is much easier to store vast amounts of fresh water (sea water is corrosive) needed for sound suppression on land than at sea, and it is much easier to transport the launch vehicle to the launch platform when the platform is on land rather than at sea.