I just built a new table, I’ll put some picks up in a new thread, I haven’t decided on a top for it yet. I was thinking this time I would use 2 layers like you are doing but maybe a thin full top of MDF to keep things square and make a solid torsion box, that a thicker MDF skin on top of it. Let me know what works for you.
I made my table such a crappy size I need all kids of 25″ and 25.25″ pieces…so much less waste if I just went with 24″ or a hair under. Live and learn
I think OSB would be good for a base but I wouldn’t use it as the actual spoil board for a few reasons. I am not sure what a good one would be except maybe something soft like pine.