First my go to tutorial for resin waterways.
https://hirstarts.com/tips17/tips17.html#waterIn the US envirotex lite is readily available at Home Depot, Lowells or Ace hardware.
In the UK I have had to order online. My last two batches were Clear Cast Alumilite.
There are several methods for creating waves. Modge Podge listed above is one. Another in the link above and the one I tried recently is UV setting clear resin. Quite a few manufactures out there so look around. In all honestly it is best to mix up the methods I will use clear resin for the base, uv or two part resin for the large ripples and modge podge for the finer details.
On the planning end just be aware that thicker resin pours can generate heat as they are curing so make sure that your materials in contact with it are not heat sensitive. I ruined a demo board that I was making that way.