Bring a straight edge with you when you find a source of baltic birch with a laminate. These are not necessarily flat to begin with. If it passes your straight edge test, it will make a good top. Angle iron takes some attention and a little lube to drill, so consider using extruded aluminum, which will be easier to work. At least the 1/8th thick, countersunk for short screws. CAREFULLY predrill the holes and keep the screws from going to far in or it will create a dimple on the surface.
Applying laminate on a two layer top would be my personal preference. Bottom layer of MDF (which is very flat), top layer of Baltic Birch. Contact cement sprayed evenly on the ply top and bottom surface of the laminate. Place thick dowels on top of the dried adhesive, then position the oversized piece of laminate on top of the dowels. Align the laminate, then remove the center dowel. Roll it using a J roller from the center, out. Gradually remove one dowel after the other, rolling center out to eliminate trapped air. If you have a bubble, you can use a pin to deflate it, or carefull drill from underneath without going through the laminate. But if you roll center, out, you won't trap air.
I think pouring a surface and allowing it to level sounds good, but I can imagine any number of things that could mess it up.
Here's a video that might help. I'd use spray rather than brushing. Make sure you let the adhesive dry completely before you join the parts.