In a very early part of the game chimecho will start its assembly. It will ring the friendship bell and you will have the ability to recruit Pokemon. It is totally random when you get to recruit a Pokemon. I don't know what the exact chances are of recruiting a Pokemon is but it has to do with your teams rank, your IQ, and if you have any helping items like friend bow. Obviously The higher the rank/IQ the higher your chances of recruiting a Pokemon are. Also if you have a higher rank and IQ you will be able to recruit new Pokemon.
Yes
he is a fake
they ask you if they can be on the tam
Nope
you recruit him by going to electric plateau
No, there isn't.
If you're talking about Pokemon Mystery Dungeon Explorers of Time or Pokemon Mystery Dungeon Explorers of Darkness, you can recruit as many Pokemon as you want. If you are talking about Pokemon Mysatery Dungeon Blue Rescue Team or Pokemon Mystery Dungeon Red Rescue Team, you can only recruit a certain number of Pokemon per friend area.
mission recruit or egg
no but you will find the statue of arceus
in the second cave
dungeon leader can be any Pokemon you recruit. you will be able to change leading Pokemon after you graduate .
concealed ruins with secret slab or mystery part