the rec is to give water in a sippy cup from around 6 months so you're pretty close.
ideally, however when you introduce solids LO may get thirsty for water and not have enough skill to use the sippy, I offered a sippy or water but also a bottle of water during solid feeds to ensure he got enough liquid. As you LO is so close to 6 months I wouldn't see the harm of a bit of water in a bottle or cup, like Erin said, watch the milk doesn't drop.
Does your LO really need the extra iron in the vits? formula is balanced to their needs and full of vits, a vitamin supplement wouldn't usually be needed until 6 months when baby's reserves begin to drop and even then the supplements are more for breastfed babies because formula already has the added vits. I thought too much iron could be harmful?