I finally finished the floors and I LOVE it!
I placed 6 millimeter underlayment and bamboo flooring over the liquid rubber layer. In this process, I have learned that I am not very good at flooring -- at least, not with used flooring with nails. I started on the corner by the lift. This was a mistake because 1) the place I start is never as good as after some practice and 2) it was not flush so it created some weird angles that skewed the rest of the floor. With the spaces it looks more like a deck than flooring, which I am actually cool with. Plus, I screwed in each plank so they should be solid in place (again, extra). I will probably research something to fill the gaps and provide more water sealant to the floors.
All that to say, I love how bright the floors look and it is all nice and smooth. So happy I found the used bamboo on Marketplace! It took me the equivalent of 2 full days spread over a few shorter days. I completed it during 90+ degree days. It definitely feels more home-like and I am now able to start moving in the base cabinets I have collected (again, Marketplace). The flooring was a bit step to seeing it come together and be my home. <3