Yeah, pine is a pain. But it was cheap, and dude who made it knew that.
The epoxy that my friend sells is pretty durable stuff. We made a charcuterie board at his shop and have used it as a cutting board. The epoxy is tougher than the walnut it is bonded to. I would suspect that a thin layer (1/8 to 1/4) would be sufficient to protect the pine underneath. However, you are going to have to pour that at least 1/16th thicker than you want so that you can sand off the imperfections. And it may be a lot more than that, as the epoxy tries really hard to seek its own level but is too thick to do so without ripples. You will also need an epoxy with a lot of drying time since the pour is so large, and a very fine-grit sand paper (probably 3000-ish) to get a really smooth finish (although I may be wrong about that).
Honestly, I would send my buddy an email
and tell him what you are doing. His name is David Goss. It's what he does. Or, at least, it's one of the things he does.
Make sure to tell him Ken Scherer referred you. I know all of the people on this page
and trust all of them.