The simple answer is yes. The voxel size of the CT scan lays a basis of the geometric information. The minimum voxel size required is determined by the clinical question you are intended to answer with your FE model with a clinical acceptable accuracy.

There isn't exact number of slices needed for making a good model. Maybe you should be concentrated on how thick the slices are. You can make a pretty decent 3D model with 1.5 mm slice thickness, but thinner the slice thickness, better the result :)