Questions about storms...

I have recently decided that I will switch my map's theme (cp_loose) which is factory-like, to a less generic one abandoned-on construction-stormy-factory. I already know how to create rain and the guttersplash, but I dont know at what distance I should place each info_particle (rain) from each other and from the walls. Also, how is it posible to imitate the thunder sound in arena_sawmill? Thanks for any answers

So I simply put a soundscape with the thunderstorm sound anywhere?

Also, how do I install the custom collision particles? I didn't understand the instructions very well...

Thanks