You don't need Starlink maritime. Get a normal "pizza box" Starlink for a lot less less. That is what I have, and sail from the BVI down to Grenada with it - getting fast and reliable internet along the way.

I have it mounted just above the bimini. The only times the 150+ Mb/s is deteriorated is when I'm close to cruise ships - they suck up all the bandwidth. The antenna wants to point roughly north and 20 degrees above the horizon, although horizontal works as well. So plan on the boat pointing into the trades and place the dish so that roughly north is as free from metallic obstructions as possible. There's no need, and only disadvantages, to putting the dish at the top of the mast. Nobody uses that, everyone just finds a location on the port side or far aft.