The picture #1 is by far the best looking of the 3 examples.
The filler pulls out the grain with the oil finish.
I would fill any small holes first, before using stain.
Sand thoroughly, but don't spot sand. Use long sanding strokes with the grain. I recommend a walnut colored filler. If the paste filler is new, it should be ready to use as is without thinning. We usually only thin hole filler after it starts to dry out.
Don't confuse a hole filler with a grain filler. Don't try to thin Famowood hole filler to use as grain filler. Two entirely different things.
The grain filler is usually sold in quart cans. Hole filler is sold in little 5 oz cans or in tubes like bath caulk.
Grain filler might need thinned down to slow drying time.
Grain filler is applied by rubbing on cross grain. Allowed to harden and rubbed off cross grain. Use coarse cloth for rubbing off. You're trying to leave the filler in the grain. If you rub with the grain, you will rub it all off. Let the he filler set-up, but don't let it get hard on you. I usually use mineral spirits for a thinner if needed. It will most likely tell you on the can. Unlike Oak or Mahogany, Walnut usually needs very little grain filling.