Its normal to worry about the next child having issues, even when they're doing great, just due to the traumatizing situation the first caused. In my case it was my daughter being an inefficient breast-feeder. She dropped down to 10 oz. less then her birth weight at 5 weeks old and we had to supplement with formula, which caused her to refuse the breast. It was very traumatizing. With my second she was a GREAT breast-feeder and gained quickly and steadily, but I was still worrying all the time that something would go wrong. You'll look back at this and smile someday, but for now, be assured that you're doing what's best for your little guy!
Until a baby is 1 year old the MAJORITY of their nutrition comes from breast milk or formula. Solids are just an opportunity for them to experiment with tastes and textures. So be happy for what he's eating, but don't feel like you have to get x amount of cereal down him. I haven't messed with rice cereal for months now (my daughter is 10 months old). She eats cheerios, and any fruit, veggies, tofu, corn or beans as finger foods I give her. She does MUCH better when she can feed herself, she enjoys stuffing her mouth and its adorable - though very messy. :) I'm starting to give her whatever I can from the table too.
Hope this is helpful! Best wishes!