Recommend the local Columbia Paint Center or Sherwinn Williams for quality stain and a pro that will listen to your project vs. the box stores with the part time employees. However, they may not be familliar with Waterlox and how to mix stain with it.
Daly's makes a good penetrating stain for soft woods (carried at Columbia). Look at thier color swatches and even ask to take some home if you need to. Bring a small piece of flooring back to the store with you (one with some character in it so you can see how the stain works with the knots and dings and stuff like that) and once you have a choice made ask them to show you that color on your piece of wood.
Take note of how long you should let that color sit on the wood before you wipe it off. Depending on the color you want, how long it sits before wiping may effect how deep or how light the end result turns out. Some stains are pretty fool proof and it isn't too much of an issue.
Possibly the easiest application (not having to worry about wipe of time etc.) may be to find a very very dark version of the color you want and add it to the Waterlox sealer. You can call Waterlox and they will have good pointers on how to do that as well.
ONLY the first coat get the stain. So test with scraps and be sure before the application. With your floor you will need a total of 4 coats if you go with Waterlox. 1st coat can be straight stain, stain w/ Waterlox Origional Sealer, or straight Waterlox Origional Sealer. Then another coat of Waterlox Origional Sealer ONLY (no stain in 2nd coat!!) followed by 2 coats of Waterlox Origional SATIN FINISH (if satin is what you want ... carry on with the Sealer if you want semi-gloss).
Mind you, there is a pretty drastic darkening that happens with the tung oil, and given time to amber (couple years) you may find the floor you want "naturally".
Adding stain will indeed show off some patina and the grains around knots etc ...
BUT staining will also do a fine job of showing off any scratches you (no offence) as a rookie DIY'er have left behind with the power equipment that was rented. Anything you don't want seen in the final product ... stain will show you.
Some of us pro's charge nearly 2X as much to stain floors due to how meticulouse the demands are. Extra hand and palm sanding are required to remove bearely visible scratches that WILL show with a stain. AND to further complicate things if you over do it with the palm sander and burnish the wood around the perimitter where the scratches tend to be
or sand un-evenly
or over screen
or...... you get the picture ... the stain will surely show you these things as well. (Skeered yet?? )
Sorry this is so lengthy but I do pride myself in qualifying the customer so the best decisions get made, and with a very wide plank floor you'd be amazed at how much easier it is to show off any mistakes that happen.
Good Luck,