It may be hardwood but it most likely - 95%+ - engineered hardwood. First 7" is not common at all for pure hardwood and would cost a fortune. Second you almost never float pure hardwood.
So let's assume it is a nice engineered floor. The wear layer on these range between 1/32nd to a 1/4" and hardly any of them can be sanded, even once....
Are you sure it’s “hardwood”? If it was nailed to a sub-base, the tongue edge would be fastened to the floor and extremely difficult to remove without breaking the “tongue” off.
I’d also check to see if there’s enough wood left from the tongue up to the surface…minus the depth of the dark stain you’re trying to remove. (Often the boards have been sanded in ...
should I RE-SAND all the cabinet doors again before I apply the final
I would. As cabinet doors they will be quite visible and I'm sure you want the best finish possible. A light sanding after the primer ensures that the primer is smooth which will help you get a good finish coat.
Also...is there any tricks to making sure I get all the dust off