Not if its not designed that way.
It has to be electric (AEG).
No. Spring must be cocked before each shot.
You kan make 1
There are too many types: airguns that are used in the auto industry, Air Rifles, Air pistols, Air soft guns.
No, only with a few Marui selected models, or with airsoft guns that have a threaded barrel of the same size.
You need both.
Yes it is possible
No. it has to be cocked each time.
No. Wrong size.
new spring or check your compression.
A spring, an electric motor or by compressed gas.
Yes, no or maybe are all correct answers depedning on how you intend to use the item. Spring airsoft guns use less parts and they don't need batteries (no need of charging), but they don't have auto/full auto capability. On the contrary, AEG's have those capability, but have more parts and need batteries to operate (hence, need more maintenance and, of course, more money to spend on it). Well, the choice is yours.