Concentraion of acid (for neutralization) is not that important, especially with a weak acid like citric acid. You can re-use your bath, so as OleTj mentioned you can use 15g per liter.
If you don't feel like saving it, a 3 or 4 grams will do. This is at least enough to neutralize a dozen or so 8x10 negatives.
Does the pH of the developer matter? I use D23 which isn't very alkaline. Others use developers which are much more so.
Actually PH doesn't really correlate to the amount of acid needed to neutralize different bases. Developers tend to have buffering agents in them as well which makes thing even more complicated.
You can tell when the base on sheet film is properly neutralized, the sheet is slippery in the developer (bases always feel this way) and when you put it in the stop, the slipperyness rapidly dissapates. If this doesn't happen, you know that the stop is spent.