Cereal is not necessary at this age, but also not a problem. The open gut refers to EBF babies and introducing solids prior to 6 months.
That does seem like a lot of solids for a 7 month old, but for dsavcom, your routine appears to be working with no wakings at night. As long as you are offering BM prior to the solids (and the solids should be 45minutes-1 hour afterwards).
Jo - Breastmilk has far more calories than any solids, so increasing cereal will not help them sleep through the night. I think you have more of a feed to sleep issue where when he wakes at night, he needs the breast to fall back to sleep. Have you tried pat/shh or pu/pd at night?