You will need a different set of gear for everything, definitely. One for tanking, one for cat dps, one for balance dps and one for healing. Druids have no inventory space free, ever.
As feral, you can tank any normal or heroic as far as I have seen, and are the perfect off-tank in raids, since you can switch to full dps when no second tank is needed.
As feral (with healing gear, of course), you can heal any normal 5man, but that's about it. As resto (or Dreamstate build), you can heal anything, but you are more suited for raiding. You can heal heroics fine, it's just that your type of healing I think is more efficient when you're not the only healer.