Coffee porter

I intend to make a coffee porter. There is a tentative recipie:
4.4 lb of pilsner malt
1 lb
0,5 lb of Carafa III
0,5 lb of Chocolate malt (450 srm)
flaked oats - 1 lb
brown shugar - 1 lb

Hops: may be chinook or something same - 1 oz for 60 min.

But what about coffee? Is it better to add coffee on a boiling or in a fermentation (primary, secondary?)? What kind of coffee is better for aromatic? How can I avoid coffee`s sourness and bitterness in my beer?

I've made an Espresso Porter which everyone thought was my best beer ever (at the time).  I added 4oz (about a double) of Starbuck's espresso to the primary as I put the wort in.

Thanks, it`s a simple method 

If you worry about oils and acids from the coffee, adding cold brewed coffee to the Primary is a good method. Just make sure the vessel you brew it in is sanitized, and if you're worried about the water, boil it ahead of time then chill it for the brew.

Are coffee`s oils negative for a stability of head?
May be are there other pitfalls about adding of coffee in the beer (in addition to acid and oils)?

The oils do effect the head, the acids can leave a bad aftertaste in the finished beer. Other than that I can't think of anything that coffee could negatively effect a beer.