The WIC office is the one who advised me on how to make the switch. We started 4 weeks before his 1st b-day. His bottles were 8oz. Week 1 - 6oz. formula, 2 oz. whole milk. Week 2 - 4oz or each, Week 3 - 2oz. formula, 6oz. whole milk, and Week 4 - straight whole milk.
At the time he would drink 5-6 bottles a day. One in the morning, one for mid-morning, the day care would give him sippy cup of milk at lunch, another bottle mid-afternoon, one around dinner, and one before bed.
We switched off the bottle at about 18 months. Had a little difficulty with that one.
As for vitamins, whole milk provides a lot. Then if your child is a good eater of healthy foods, she should be getting what she needs. Our pedi always recommends a multi-vitamin for children, especially ones who don't eat well, to supplement what they may not be getting.