No need to sharpen the edges. Just triangulate the lowpoly before baking and make sure to use that same export for previewing too. The baking lowpoly and preview lowpoly must have to have the same triangulation, otherwise these kinds of errors will show up.
A lot of those errors, specifically the "x" shaped ones are happening because you didn't triangulate the lowpoly before baking. Different softwares tends to triangulate the mesh differently, so its important to triangulate before baking, and then use that export for previewing too. Also, the lowpoly vertex normals ARE…