Let see yes over prolong time magnets can decrease their magnatism depending on such factors as the material of the magnet and the surrounding temperature and so on.
No it does not need to take energy to remain at some position in the gravity field.
It take force on the object equal to the gravity field force at that point and the force can come from the walls of a building or a magnate field or air pressure or...............
To change the position of an object in a G field does take energy or yield energy for example climbing the steps in a building with a weight take energy.
Ok force and energy are not one and the same thing and you can have forces on an object and have zero energy.
Lord to explain this fully you would need to give a 101 physics course and cover such concepts as force and potential energy and that work equal force over a distance and on and on..........
Sorry you need to take out a few books that cover newton physics from the local library.