Nikon are by far the best microscope for they allow crisp viewing.

Objective lens will sometimes transfer from one microscope to another but not not always. I would only get the objective lens for the microscope brand.

Oil Immersion - 100x lens:
Prepare your side and drop a cover glass on it.
Then drop a bead of immersion oil ontop the cover glass.
Dip the Objective lens into the oil. You should not worry about breakage. If you are breaking the cover glass then your focus or adjustment may be off.

Remember to clean the oil off the lens after each use so you don't get a build up on your objective lens.

Tammy