Starting cereal/oatmeal

Hey ladies!

Ftm here and a few questions about starting my LO on solids. He will be 6 months on the 24th. We are going to start him on oatmeal/cereal today to get him used to the texture/swallowing, and just wondering how you mamas went about introducing solids while still doing milk?

He typically drinks 6 oz every 3 hours (formula fed). My plan is to do some oatmeal in the morning and then more at night with his last bottle. I know he should have a bottle first so he's not overly hungry while eating the oatmeal since he will be getting used to eating it. My question is, do you ladies reduce the amount in the bottle you give you LO when they are eating solids? I don't know how much is actually going to make it into his belly, so I don't want to reduce the amount in his bottle and have him be hungry. However I also don't want to over feed him and give him a belly ache!

Any help is appreciated!!