[2022] How to make a base

For the floating problem, I advise you to stick with the default, full sized block shape for your first construction. They take up an entire voxel, so there will be no floating, and you can get a sense for the size and alignment of voxel space. For the unevenness with the ground, the most basic solution is to build your floor on top of the ground, instead of trying to build it even with the ground. There are ways to get more fancy/pretty results, but I’d go for clean and functional for your first days.