I'm not sure I agree with your doctor that you need to add fruits and vegetables yet. The others are right that they need only milk or formula until six months or so. One question, did your little one express any interest in solids before you gave rice to him? The pediatrician we had in California before coming to Colorado told us to give our boy solids when he "asked" for them. The reason that you don't feed solids too early is that there are litterally microscopic holes in the intestines of infants, through which food molecules can pass, and this is thought to set up the process for food allergies. Their gut isn't "closed" until at least six months. That said, I'd stick to the breast as much as you can, formula, and rice for now. Breast milk is amazing... it changes in composition as your little one's nutritional needs change. But, if you do want to go ahead with solids I suggest going in this order: Orange first, then green. You are just in time to start with the orange: winter squashes like acorn, butternut, etc, and sweet potatoes. A couple of teaspoons is all he needs. I suggest making your own by baking the squash or potatoes, puree in a food processor, and add breast milk (if you're pumping) or a bit of formula to make the consistency smoother and softer. Another thing you can start before greens is mashed bananas or avocados. Both of these are great, high in minerals and GOOD fat that will help put weight on your little guy. Bananas might cause some constipation, but not if you're giving only a little and still plenty of time at the breast. After a a couple of MONTHS of orange, start on the green. This is because the orange stuff is easier on his gut than the green. When you start green, steam peas, green beans, summer squashes, etc. until very soft. Puree and add milk/formula to a good consistency. I bought a bunch of little tiny Rubbermade containers and put the purees in those. They were just enough for one serving, and I could do the cooking once per week. This was really helpful because I worked at the time. If you cook the food and put it in little containers, then you can put them in the fridge for a week. Since you do it in small portions from individual cups the food is not exposed to anything until you are ready to feed your son.
My son had a rough start as he didn't nurse well due to minor deformities in his mouth. He was supplemented with formula after EVERY nursing session. He wasn't declared a "well baby" until he was about ten weeks old. Our pediatrician in California was very supportive of my desire to nurse, and even though my little guy was skinny for a LONG time, he didn't push solids. Now, my little joy is healthy as can be at two and a half. The Cali doc was a little bit older, about 50 or so, but not so old that he was in the school of thought of starting solids early. I think the advice he gave to us was wonderful, and our boy has grown big and strong and VERY healthy!
One more thing, it is a myth if you start with fruits that you'll never get your baby to eat vegetables. Our California doc explained that fruit has such a high sugar content that is is difficult for babies to digest. Like most kids, my son ate vegetables for quite a while, and then decided he doesn't like them now. I keep offering, and eventually he'll take them up again.
As for schedule.... we gave our guy solids only AFTER nursing, just twice per day to start.