The only thing I can think of damaging, is if you have a bargain basement Remote Start Kit, and it grinds the starter when starting the vehicle, or when you turn the ignition on after the vehicle is running. I have seen this, and it'* not pretty. But, if you bought a higher end model from Viper, AutoLoc, AutoPage, etc.. you won't have a problem as far as that goes.
They will damage the vehicle'* electrical wires, because you have to cut and splice them, but that'* true for ALL kits.
For the install, if you are buying one from x store, it will probably be cheaper, than if you were to buy it from x store, and bring it to y store and say install x store'* product. If you are good with electronics, I am sure you could do it yourself. There is TONS of info right here on BC, not to mention other resources like The 12 Volt
. And I am sure there are many others.