The surfacing of the table continues. Drying has been painfully slow due the high level of moisture in my basement right now (long story.) I bought a couple "Damp-Rid" or something tubs and they are actually sucking the moisture out of the air. They are surprisingly effective for their size. Drying is important because if you brush over areas that are semi dry they will pill up and pull off the wood. I've been able to fix those places by tamping with a damp sponge to make the surface flat but rough again. It seems to have worked. I'm happy with the texture too. Some of the largest bits in the sand (small rocks, really) stick up too much, but you can just pop them off easily. I have yet to give the surface a stress test but I'm hoping it's fairly durable. If not, maybe I can coat the top with polyurethane too. I think Future floor polish might do the job too.
The 32 oz jar of spakle I have been using may not finish the job. The technique I am using to place the sand down now is the most efficient for spackle to area ratio, but some earlier areas used a fair bit more spackle than I should have to stretch the 32 oz over the whole table. If you want to emulate that technique, the thinned down spackle + sand mixture is about the consistency of melted Cookies 'n' Cream ice cream, and it brushes on nicely.
For this initial surface I am loathe to do things like place lakes or rivers (or any permanent landmark for that matter) because it changes the nature of all games played on this board. That's what the foam boards that lay on top are going to be for. I bought 6 4'x2"x1/4" pieces of wood to make the borders. They will get glued to the outside of the 1/2" plywood, so 1 1/2" of border will stick up around the table. I'll be using construction adhesive to glue them, which is really amazing stuff. I was hoping to mitre the border pieces, but in the end using the 4' length of pre-cut will mean the edges will meet at a square. The 4' pieces match the length of the 4' side of the table and they would need to be a tiny bit longer to mitre. No big deal.