Not great idea. The traditional time to start complementary foods (like cereal) is around 4-6 months, when babies have developed the oral-motor skills to handle them. Giving cereal earlier than this may increase the risk of obesity. There really isn't any need for complementary foods earlier than 4-6 months.
It's better to wait. Starting rice cereal before 4 months old increases the risk of developing an allergy to rice. This applies to starting any solid food this early;your baby might be stuck with that food allergy for life. Unless your baby's doctor says you need to for a specific medical condition, it's best to wait til 4 months, then give solids by spoon, not in the bottle, so they can learn to eat & not drink them.
No. Why? Why? Why? 8 weeks? Not 8 months right? You really meant 8 weeks right? No.