This is getting complicated.
The figure for open circuit flux on the face of a magnet is no use here. basically all neo magnets can produce something like 1.2T into a closed circuit, depending on grade, but that is near enough.
The flux you get in a machine depends on the relative length of the magnet and the air gap. With an air Gap about magnet length ( typical axial ) you will have a gap flux of 0.5T. if your air gap is short compared with the rest of the magnetic circuit you will get higher, right up to 1.2T when the air gap is zero.
For a motor conversion with decent thickness magnets and a small air gap you will get something under 1T. This will only change a small amount with different grades of magnet. Typical neo N40/N42 will be fine and probably something over 3/8 thick to deal with a practical air gap. N50 will do a little better and cost a lot more.Those you are looking at should do well enough just forget the gauss on the face and lifting force, both figures are meaningless except as a direct comparison of similar size magnets of different type.
What you calculate from the emf divided by the circuit resistance is short circuit current and that is no use to you. As I said you need the voltage driving the current through that circuit resistance, the battery internal resistance is so near zero that you can forget it.
Flux