In the area where the cheese farm is. Jump around towards the back wall and the B lightbulb will apear. Conker will turn into an anvil, break a wall and the tail there gives 10 extra lives.
To avoid ever losing the Bomb Run mission (according to the time limit), just enter a new area along the path of the designated point. Once you enter a new area, you'll experience a brief loading scene. Afterwards, you can quit game, re-load it, and you'll end up in that same area, along with a refreshed time. Repeat as necessary if you're running out of time.
You can unlock Potty Mouth by beating the Single Player or by having all 6 Class Medals
By playing online and winning, you'll be able to unlock upgrades for your character.