How much sauce do you need per person?
There are a few factors that could effect this:

1) How the meat is cooked and how lean or fatty it is. If you overcook the meat (although I doubt that you would!) or if it's leaner or fattier. If its a fattier meat add say an extra 2 tbsps or so of sauce and if it's leaner (or overcooked) I would add a tbsp or so less of sauce.

2) The viscosity and composition of the sauce. If it's a white wine sauce (thinner, less rich) you would want to add more, however if it's a hollondaise sauce (thicker, richer) you may want less.

3) Opinion, some people like more sauce, some people like less. It may depend on the type of sauce which you may want more or less of.

Saying this I would say around 4 tbsp of sauce, then account for the additions and your own personal preference. Any more sauce and it may become swamped, any less and you will not have enough sauce to taste or keep the meat moist. It is a very subjective subject so do keep that in mind.