I wonder how much is the salary for a houseboy and that amount is paid for what specific of duties they must do? How if you ask the houseboy to do something out of those you listed as duty?

that's totally up to you to negotiate.  it's usually room & board including utilities & meals out, sometimes other expenses, sometimes travel or entertainment.  but i have heard of and also been offered situations where i am expected to pay rent & my own food ranging up to situations where there is a salary for additional work.  it depends on how wealthy they are and is more likely if it is a couple or trio vs a single guy unless he is very financially well off.  

the stories i hear where things go wrong are usually when the employer is trying to entice a young hot thing with an offer of lots of money, and he ends up being lazy, and the host doesn't have the desire/willingness to discipline him & get him back to work.  and then things go south and he gets kicked out.  

longer term situations that are successful cover the whole gamut but seem to tend to where the houseboy has some kind of independent income stream, usually part time.