I suggest, block your whole island out first, keep basic generalized shaping for it and get your game working.
In industry, this is called “white boxing”
You can then use that generalized shaping by either manually painting it in after the fact, but you can also do some fancy things where you blox to create your terrain.
Either way, I highly suggest that at every step eliminate any unnecessary blockers that can be filled in after the fact once you get things working. Really assess what is needed at the time and if it can be done without till you ABSOLUTLY need it. This will increase your chance of completion of a project 10 fold!
Check out the assistant, it can give you ideas for builds if youre unsure how to start–or are new to building. However other people here may have fantastic advice!