Should be bolted from underneath. As far as the holes it depends on $. Best option is bondo and paint. Could get creative like an 8 ball or boble heads but you would have to make sure it is strong enuf. If the spoiler is just damaged you may be able to get another at a junk yard.
The holes with some rubber push plugs and you could fill the car.
The holes with some rubber push plugs and you could fill the same color as the car.