If you are a pessimist, our worst case scenario is none. Not because we are a bad team (we've clawed our way up to be one of the top 7 teams in the NFC right now in my book) but because we have a tough schedule and the teams we should be favorites over are all away games, teams we are underdogs will be at home.
If you think we've crossed the threshold into full-blown good team territory, though, then 4 games is actually a realistic assessment.
If you just want to go based on who we SHOULD be favored, than the number is 2.
The by far most important game on the schedule is this next one. If we win that one, we are probably favorites to make the playoffs, even if we only win 1 more game. If we lose, we probably need to win 3 out of 4... which means beating at least one of Packers or Vikings.
If the Cards weren't at home, we should be considered the favorite--but the home field advantage is enough to push it into 50/50 territory.
Big game.