Có phải chất tẩy biểu bì là thứ nhất định phải có không?

Or is buffing the nails with a 240 buffer enough too?

A cuticle remover is preferable, or even a careful removal with a cuticle tool. It is skin (non-living) and is too soft to be efficiently removed with a buffer. Plus, the nail plate could be over buffed. Just remember to remove it in the appropriate way and make sure the nail plate is clean and dry.