What do each of the actions increase, numerically?

The following have been determined experimentally.

We have four primary indicators: Questions, Answers, Users, and Quality.

Every day, apply a decay point to each indicator. If an indicator has any hearts, and it reaches two decay points, remove a heart and clear the decay point. If it has no hearts, and it reaches three decay points, it now becomes red. If it has no hearts and reaches eight decay points, a flag MUST be used or the game is over. (If you have no flags then it's an automatic game over.)

Each indicator has an associated action. Ask with Questions, Answer with Answers, Upvote with Users, and Downvote with Quality. Taking an associated action will clear the decay points, add a single heart, and protect the indicator from a single decay point.

Taking the associated action when an indicator is already at four hearts applies a buff point. A single buff point will protect against two decay points, but does not factor into site progress or indicator interactions. (This means that the chosen indicator will resist three days of decay before dropping by a heart.)

(Interactions between indicators, as well as the effects of Downvote, Close, and Flag forthcoming.)

You've got it almost correct; the only difference is that Downvote decreases Users by exactly 0.5. Also, it should be noted that there is another action that appears after graduation: Close. Close does -2 to Questions and +2 to Quality.