I will try to answer your questions as best as i can.
Airsoft guns are like bb guns except they fire a plastic bb, some of different larger sizes.
There are different systems for airsoft. Electric and green gas are a couple. The electric is simply a small motor that spits the plastic bb's out of the muzzle. Green gas is like a Co2 bb gun and use compressed gas to propel the bb.
Though airsoft guns dont have the velocity (at least the ones i have experience with) of say a bb or pellet air gun they are not toys, and have the ability to hurt someone (yes they can sting) and probably would not suit your intentions.
The electrics have no recoil and i doubt the green gas ones have much, if any.
Dry firing damage? Electrics, no wont hurt it. Green Gas, possibly because of the seals they utilize being its compressed gas.
Adapting to another firearm? I suppose it might be possible but might not be worth your time, expense and effort if in fact it can be done?
Hope this helps. Good luck