The quality of the audio output of a VHF radio has nothing to do with the quality of the antenna. It has to do with the audio circuit of the radio and the speaker.
It is possible to adjust the frequency response of both the audio circuit and the speaker to emphasize the frequencies where...
Remember that if you store your dinghy on your swim platform, you will no longer have an available swim platform. You may not be able to climb back into the boat if you fall into the water and you won't be able to enter or exit the boat via the swim platform at docks or marinas.
Think about...
If your boat has internal potable water tanks, fill them and just use your water system and pump as you normally would.
There is no need to turn the pump off.
Some people have appliances on their boats that require 120 volt (or 240 volt) AC power to work. Air conditioning, large refrigerators, washer and drier, etc. They typically run a genset 24/7 unless they are on shore power.
What you are missing is that charging a battery takes power from the engine that would otherwise be used to propel the boat. A 200 amp alternator would use considerably more power than a typical 60 amp alternator.
Driving the 200 amp alternator would also require more and heavier belts to...
PLEASE! Back away and put the wire cutters down. Get some competent help with this replacement. If you don't know what you are doing, you could make a mistake that could be lethal at some point.
There is no shame in hiring a pro to do what you don't know how to do and you aren't going to get...
I think you will find that many of those "no-wake" zones are bogus signs put up by waterfront homeowners and can (and should) be ignored. Look for the official state logo on any no-wake sign or buoy.
You have the option to contact a different company and see what they have to say, but nobody on an Internet forum who hasn't inspected your boat can tell you if you need service ports in your tank.