Refinishing / finishing out Douglas fir
Is this Douglas fir?
Everywhere there is carpet in our "new" (1945) house - which is pretty much everywhere except for the kitchen and baths - looks like this. The carpet is ancient and incredibly awful so it's coming up.
Some of it was finished at least somewhat during the construction phase, and looks like this:
The rest of it is unfinished, planed tongue and groove. It's very smooth for the most part, but I assume I will need to sand if only to expose new wood.
Orbital sand w. 150 grit? Waterlox? Some of the boards are a little loose and the ends stick up a little. Should I nail the tongue side down, or is that a bad idea? The stuff that has been lacquered already I assume I will have to take down to bare wood.
Any tips for this particular scenario would be appreciated. TIA!