Did you end up using weathered oak in your red oak floors? How does it look?

If you like dark and dramatic floors (and a dark home that needs ++ lighting) then go for it. Remember: dark floors = dark home. If you have HUGE amounts of windows and HUGE amounts of lighting (house is already lit like an art gallery) then dark floors won't have much of an impact. Yes dark floors SHOW the dust and the dirt (just as Patricia points out). The dust/dirt will be there whether or not can SEE IT is another matter. A natural coloured floor HIDES the dust that is there. Again, this comes down to PERSONALITY traits and likes rather than 'harder to keep clean'. They are just as easy to clean. The difference being harder to keep LOOKING clean. Yes dust can settle inside of an hour...making you feel like you haven't done a darn thing (even though you just swiffered). I like Bona Traffic HD for the finish. It is tough as nails and will not yellow or amber. The finish is what causes 'orange'. The water based stuff like Bona Traffic HD will not turn the orange tones you are trying to avoid.

You want to avoid applying a second coat of stain. It will cause adhesion issues. What you can do is add some of the stain to a oil base poly, then apply it. Another option is to use poly shade in a similar color. You can apply 2-3 coats of the poly shade to achieve your desired color. Poly shade is oil base. Contractor should have water popped the floor prior to applying the stain. The color would come out darker.

"considering medium brown/weathered oak chesnut/weathered oak" Isn't that what is in your second photo? You say "my flooring guy is pretty useless coming up with combos on his own", but it looks like your second photo shows he is providing what you are asking for. Your top photo is not "medium brown/weathered oak/chestnut". I think the flooring guy is giving you what you asked for, but what you asked for is not what you actually want. Show him your top photo that you posted here. Here are photos of chestnut stain on white oak and weathered oak stain on white oak (a much more gray finish than it sounds like you want). So you need to give your flooring guy the correct instruction of what you want, and not blame him when you do not.