Reddit mentions of OSMO Top Oil Satin

Yeah, Osmo Top Oil is a blend of plant-based oils and a wax that have been heated to polymerize. It is supposed to be amazing.

Well, regarding the sanding, my rule of thumb is to sand moving up through the grits until the sanding marks disappear. How high I go with the grits depends a lot on the tool I'm using (hand sanding versus orbital sander versus random orbital sander),species of wood, and what finish I plan to put on it. Hand sanding following the grain is pretty forgiving, because the scratch pattern blends in with the grain. Orbital sanders tend to leave a scratch pattern across the grain which stands out. Random orbitals are better, but still leave some swirls across the grain. If I'm going to stain it, sanding marks will show up much more strongly than if I was just going to clear coat it. Every project is different, but typically I'll sand to at least 180 if I'm staining, and at least to 120 if I'm just oiling and clear coating. In truth I usually go higher than those numbers, but if I'm in a rush I can get away with those as minimums. I've used it on a couple of projects and have been quite pleased with it.

Now, all that said, the amount of sanding you do doesn't really change the porosity of the wood. Rough sanding will leave a more toothy surface, but that doesn't make much difference to an oil or other penetrating finish, because it will soak in as deep as the cell structure of the wood allows regardless of how smooth it is. Paints don't penetrate, they just cling to the surface, so leaving a more toothy surface does benefit them. I looked at the primer you linked, and I'm still not quite sure what to make of it, but it seems to me to be something along the lines of what I've seen called grain conditioner, which is basically a thin oil that penetrates and soaks into the wood to sort of level out how the wood absorbs subsequent layers of stain or dye or whatever. It basically helps prevent blotchiness. Since it is a penetrating substance, it shouldn't really matter how much you sand it.

Since you seem to be having dificulty finding a final finish, I might suggest OSMO Top Oil. It's a hard wax oil that both penetrates and leaves a wax film on the surface. It's meant specifically for kitchen countertops, so it should be able to handle hard use and abuse, and it's easy to apply more as it wears over time.