The person at Home Depot could not have been more wrong. This is a perfect example of the big boxes providing the exact opposite of the correct answer. We should never expect paint to have any ability to fill anything. There are high build primers on the market and even those have a limited ability to fill. If anything, paint with a sheen will highlight the grain instead of making it go away.

Not easily. Paste filler is used to fill in grain but it will not stick well to already finished surfaces. Even if you sand off the existing finish, it will still remain in the pores where the filler needs to stick. You can minimize the grain by sanding, but few finishes are thick enough to cut back from the flat parts of the surface and leave the grain filled. The only real way is a compatible top coat and sanding back.

I have decided to try again and refinish the floors in a few years after I add new flooring to the main level of my house. So I am going to try to mix a one-coat stain for the stair treads. I'll try minwax red oak and espresso first. I might buy a dark walnut or other dark color stain if that doesn't work. When I refinish, I will probably build new flush-mount vent registers and toss the ones I have. They are not that well made nor structurally strong, especially at the intake. (I keep stepping on the edge of the vent register in front of the patio door and I'm afraid I will break it.) But I will keep the registers I have until I redo the floor. I think I need to frame out the vent openings with mitered floor planks and run the register slats across the shorter dimension. Two more immediate concerns: (1) Stair Tread Project: The varathane water poly on the wood floor is being scratched from the dogs' nails. The scratches are white-ish. I have been letting the dogs play and I need to do a better job trimming the puppy's nails. However I do not want to deal with scratched poly on the stair treads that I will be installing soon. Do the scratches come out when you sand-screen and apply a new coat of poly as maintenance? Or should I use a power buffer? What tool would you recommend? I prefer not to remove the white painted side trim when I refinish the stair treads every couple of years (as necessary) because it will be thin and will probably have to be replaced (and it will be hard and time consuming to cut new trim pieces). (2) Fireplace Project: I will be re-tiling the fireplace hearth this year. The hearth is framed by wood flooring that I just refinished, and will refinish again. I purchased carrera marble tiles, about 3/8" thick. The marble hearth will be flush with the wood floor. How should I tile this so that the marble is protected when I refinish the wood floor again in the future? I don't want metal edging between the tile and the wood. I sealed the inside edge of the wood floor that surrounds the hearth with poly already, and I won't be changing the color of the wood floor significantly.

I think it's hard to tell whether either of them would look good without having a picture with them next to your other selections in the same lighting. However, trying to compare them to your other pictures, I am worried that they are both too dark for your cabinet choice. What is the tile installed in that kitchen picture? That color tile looks nice with the cabinets, but your choices look much darker than that tile (it could be the different lighting though). If I were you, I would go with the gray tile you originally chose because (1) it's lighter and therefore I think it will look better with your cabinets, (2) it's less patterned, and therefore less likely to look busy with your counters and carpet, and (3) I think the simple gray tile will stand the test of time better than the wood look tile (which may have a fake look next to your real wood cabinets).