C.H.
You probably do want to call your doc's office and ask how important the cereal is. I don't think it's a very big deal, but it does have the iron for babies who are getting ready to be on the move. However, it does sometimes take A LOT of tries before a baby will eat something new. So, don't give up if you've only tried a couple times. I've heard it can take up to 15 times of trying something new.
My son has a sensitive tummy to and he didn't have any problems with any of the vegies (except of course those he didn't like). Generally, sweet potatoes and squash are well-loved and easy on the tummy. For some reason, carrots commonly do cause a slight rash (according to my doc), so just pay attention after you start this one. Both of my kids got a rash with carrots for a while. Have fun - this is a fun time!! It's great to watch their little faces when they taste something new - good or bad!