the serial number on your ruger P345 is located on the right side of the firearm directly beneath the slide. its a silver looking plate with an 8 digit number.
Take it to a gunsmith. You did not say what is wrong with it.
100-400 USD or so
100-400 USD or so depending on specifics
if you mean the air soft pistol then yes it can take both 0.12 and 0.43 plastic bb's
Moondog Industries gas fill O-rings from evike.com. Quick, easy, and inexpensive.
No such Ruger ever made
neither, also it doesn't matter which one is "stronger", if you have a a high FPS (strong), you can't play on fields
Can't be answered with just that information. Which Ruger?
First off, it's "picatinny" rail. Secondly, no there are no aftermarket rails for that model that I am aware of. However, a competent gunsmith may be able to machine the frame to act as such.
Not a complete question.
100-300 or so