I've installed 5'' BC planks and am in the process of finishing. I've drum sanded with 60, 80 and finally 100. I edge sanded with 60 and 80.

I have a few questions:

What grit should is appropriate when I use the buffer?
What finish should I use? (I'm a DIYer and am thinking of 2 coats of semi OMU and a final coat of satin OMU)
What method of application would be best for 300 ft²?

I would appreciate any advice.