I am currently on act 3 and have been using a 2 handed weapon through all of inferno. Here is my suggestions for minimum resistances for each act.
Act 1 0-300 300+ ideal
Act 2 300-600 600+ ideal
Act 3 600-900 900+ ideal
Act 4 900-1200 1200+ ideal
You also need to have high armor and a decent health pool. Most of the armor I buy from the AH is loaded with resistances and +armor. Sword and board is NOT required, it just makes progressing easier since you can add to your resistance/armor gearcheck whereas you cannot with a 2 hander or dual wielding. If you are finding the content too hard, it is because your gear is not up to par. This is a gear based game.