As long as you are not planning to do the laundry at night while you sleep it should be fine. Ideally the laundry machines should be accessed from the hallway, and not from the Master Bedroom.

I think it would be fine, but I would caution you to keep everything off the floor in the closet, including shoes. One washer overflow or broken hose could ruin an extensive (expensive!) shoe collection.

If you have children, sooner or later they will want to wash a favorite shirt at 2 am or discover that they forgot to dry their clothes at 6 am when they are leaving at 6:50 am on a field trip. Access to a washer and dryer should be from a hallway and not share a wall with a bedroom.

Also, I wouldn't want all that humidity from the dryer in my closet. Not great for your clothes and shoes. You would need really good ventilation for that to work.

This is actually a second washer and dryer for our home. Our full size laundry was great for the family and still is for my husband's really dirty clothes but we now have an empty nest and our master bedroom is on another level of the home. I seem to struggle to get dirty clothes upstairs and clean clothes back down to the closet! I have become lazy in my old age:) I am concerned about the ventilation and the noise. Are the front load appliances noisy?

There is no reason why a washer or dryer cant go into a closet. You might want to look into one of the LG units which is a washer and dryer in one machine. It uses some sort of condensation collection to get rid of moisture, opposed to a standard vent. - the drawback is it takes like 3-4 hours for the whole wash/dry cycle to complete. Its also very small, so as a secondary machine it might work.

If its built properly it should be put in a little tub in the event it should leak. Also maybe behind a cabinet door to make it look more built in. I wouldn't worry about noise, just be concious on when you plan to use it.