4.5 to 5.5oz of sugar(corn sugar) is what I use for my beers depending on volume of course! I like a good amount of carbonation though. I do not brew to style guidelines unless I am entering a contest. I brew what I like and if others like it then I am ahead of the game!
I prefer to weigh my sugar, it gives more accuracy and better consistency when priming but that is what I do! Measuring cup is good too!
When adding the coffee, if you are adding a lot like a half-gallon or more then you may want to recheck your priming sugar amount but if it just a few cups, I would not add more sugar.
One nice thing is if you make detailed notes and do not like the results of this batch you can always adjust for future brews!
Good luck and keep on brewing!