I’m pretty sure his material setup is completely procedural so you could import your own heightmaps and this will just work out of the box. Correct me if I’m wrong though.
On a separate note - your island stuff is very interesting and the progress you’re making is great, but I live next to a beach and the tide looks way different than what you’re working towards. Right now it looks like your water level goes up and down uniformly to fake the idea of the tide going in and out. An actual tide will crest somewhere in the water where it’s 3-6 feet deep (average), fall into itself, then create a foamy wave that’s physically higher (deeper) than the rest of the water. This wave gradually flattens out as it covers more of the shore. There’s velocity to that as well - it speeds up as it gains momentum then dies out at the very end, then speeds up when it comes back. You could use displacement for this effect since collision isn’t necessary.
I’m also going to second the above guy’s post request. If your material is 100% procedural (like your others) then there’s no issue on the size of your islands, but I would want textures for valleys, plains, mountains, jungles, etc. in addition to the rocky/dirt textures you have now.