After reading up on space warfare for a while now, I'd like show how I imagine a realistic depiction of lasers in space combat. This question is more about the general perception of lasers the characters and audience will get than their physics. Please correct me where I'm wrong, but do not change my basic assumptions unless they are fundamentally flawed. Should some things sound like they are rather on the optimistic side of technical possibilities, that is because my setting depicts the far future.
Two basic types of lasers are used. Continuous and Pulsed beam. Continuous beam lasers are pretty weak unless they use vacuum frequencies (some UV, X-ray, and gamma), you have a large waste-heat management advantage (shooting from an ocean planet at an incoming fleet) or the laser is ridiculously powerful (a free-electron laser installation meant to push interstellar spacecraft up to several percent of light-speed). Pulsed beams generally give you better penetration and allow you to use longer wavelengths. They are preferred over continuous beam variants as weapon systems. Range and spot-size are improved with a shorter frequency, but shorter frequencies reduce laser efficiency leading to more waste-heat. Spot-sizes range from the centimeter to the meter range. The heat economy of lasers in the setting is generally worse than that of kinetics, resulting in large radiators laser-equipped vessels have to carry.
Lasers ruled the battlefields of space for centuries until near perfect wide spectrum mirrors capable of reflecting anything from IR to UV with high efficiency were invented. (This is a black swan technology no-one really expected and is an integral part of the setting.) These mirrors aren't magi-tech, but they are very good. Bottled light and laser defense are possible but hardly perfect. This reduced engagement ranges and made missiles and kinetics important in space warfare.
Battle craft design is still dictated by the need for laser defense. Plasma shields (plasma windows) (the closest thing the setting has to energy shields) are a first, mobile layer of defence. They are projected towards the enemy when laser fire is expected, but block all vision of the enemy and can be overwhelmed by lasers. Kinetics don't really care about plasma shields and are used to counter them. The hulls of the ships are covered in layers of the near-perfect mirrors which are cooled to reduce the efficiency loss and act as a whipple shield as well. The armor is sloped to increase the spot-size any hitting laser-beam will have and rotates quickly in order to always present unused armor to the next laser strike or follow up pulses. The last kind of defense is a mass or rather an ablative shield. It is a big chunk of ice and carbon materials, which is mobile and positioned where ever it is needed to block enemy fire.
Attacking lasers attempt to degrade the mirrors by heating and vaporization. Cooling and automated repair mechanisms attempt to counteract this. The lasers usually win, but battles can last a long time.
One doesn't see a laser in space except if you are just a few degrees off the firing axis. In that case, an observer will see the beam as a "muzzle flash" coming from the direction of the firing spacecraft. The other case where one might see a laser beam in space is when it travels through a cloud of gas. This could be leaking atmosphere or propellant or plasma shooting into space from a laser hit. Laser hits will create a bright fountain of ejecta.
EDIT1: Clarification after an answer pointed it out: You will obviously not see anything unless the laser is within a wavelength you can perceive (in the far future that doesn't necessarily mean visible light) or something is heated to emitting photons at these wavelengths.
I'm not sure how a laser hit will sound inside a hit spacecraft which wasn't destroyed by it. I imagine it will be a loud bang as the vaporized material will expand expensively.
Are my assumptions, especially about the visuals and the sound right?