That looks pretty much on what I did when I did my sink about eighteen (has it been that long?) years ago. I wound up using fiberglass fabric over the plywood, and then did a lay up of grey epoxy over that. The fancy stuff was to use Durham's Rock Hard Water Putty to avoid the perpendicular joints inside the sink to keep the fiberglass fabric from breaking.

You may not need all this, but that is what was available when I built my darkroom.

Use thick plywood. I did not, and it did warp some.