We have butcher block counter tops including around the sinks in the kitchen and the bathrooms. I used Waterlox on all of our butcher block counter tops two years ago. We loved it at first. But after 2 years it has some deep stains that can only be removed by deep sanding down to the wood. This brown stain is caused by getting baking soda based cleaning and bathing products on the surface especially around the tub and the sinks. This causes a medium brown stain wherever the baking soda water splashed onto the surface that must be sanded out. There are also some light colored stains around the sinks that I don't know what caused them. These look like water marks, but I don't think they are caused by water. Possibly these are caused by splashing mouth wash containing alcohol, but am not sure. I would not use Waterlox again if I had to start over. I would use an oil based exterior poly urethane made specifically for wood floors that can also be used on counter tops. Just my opinion. Try a small spot to experiment.

Yes and yes. I would sand the poly very well and prime it with a bonding type primer just to get the best adhesion possible when you are ready to paint over it.

Water-based all the way. It is 2020 and to me there isn't really a need for oil based products anymore. There are plenty of water-based products that are availably and are quality products. Not sure of your location and what stores you have access to but I would imagine there are options available to you. Water-based all the way though.

I have new hardwood floors in my kitchen that got stained the same color as the adjacent existing hardwood floors in my house today. The existing floors were done 10 years ago and had an oil based poly finish. Thinking about using water based poly on my new kitchen floors. Bona Traffic HD. My concern is they may look different in color from the rest of the house. Could the water based poly do that? I used espresso and Jacobean on both. Thanks so much!