Hi Adam,
Congrats on the new boat and adventure!
The HD1 Dome Pro will work around any antenna length cable issues. I’ve tested it and it is a very nice product, very similar to the HD1 Dome I reviewed a couple of years ago. They have been around a number of years, and I used them extensively on my on boat for several years. The Dome Pro has a WiFi radio in it, which is a new feature, and of course the 5G radio.
Not sure I understand your question on a 20’ antenna run?
The mini SIM injector could definitely work for you if you are using the dome.
There are some random Peplink products that support eSIMs, but for very specific reasons. Their general routers do not as far as I am aware.