Item 1: Laser light is very bright and highly focused. DON'T look directly into the beam or its mirror reflection. Diffuse reflections, such as from your finger, are not harmful and are, in fact, helpful in alligning the apparatus.
Item 2: Due to the length of the optical lever arm of the long beam path, building vibrations will cause the beam to bounce around. Anything you do to make the building shake, such as jumping or banging the table will make the beam bounce even more. The place which is most sensitive is the wall which supports the laser and the beam splitter. Any serious bump here might necessitate a major reallignment of the apparatus - about a half hours work.