For the bomb site jus' make a brush (the size you want your bomb site to be), and tie it to func_bombsite.
The terrorist automatically, at random, spawn with the bomb.
And, would you please restate your last question.

Didnt find it in faq

Q: How do I make things break when the C4 goes off?

Create a func_bomb_target where you want the terrorists to be able to plant the bomb.
In its properties set the target to multi.

Make a multi_manager and give it the name multi, disable smartedit and press add. In the 'key' field write exp and in the 'value' field write 0.
Press add again, in the key field write brush and in the value field 0 again.

Select the brush that you want to blow up, press ctrl+t and select func_breakable from the list. Give it the name brush. In the flags check trigger only.

Make an env_explosion inside the brush, name it exp and set the magnitude to wahtever you want.

It would be player_weapon_equip I believe.