Still better than the hopper. In short yes you are over thinking it. It's not a bad idea, but coffee bags do a pretty good job at keeping beans pretty fresh and brief opening for dosing shouldn't ruin your beans. If you want to go to the next level, predosing in vials and keeping them in the freezer is the next step (doubt you'll notice a difference though). I think vacuum packing is over rated and seems to suck some of the volatiles out rapidly and can actually flatten flavor profile a little. If you are fixated on the hopper solution and think that it's well sealed enough that something on top of beans would make a difference I would just spray some argon on top.

Maybe just subdividing a little? I was thinking of, like instead of separating out each single dose, separate the bag into 4 day jars, so it's less work on the dividing side but also less oxidation of the beans overall? For you, I think you gotta just try it with the rice and report back. You gonna use a sealed bag on the rice like a ziploc? Or something stretchy but permeable and rely on the rice mass and displacement to slow the air?