Those who begin early are asking for trouble. So many shaalos come each year when people try to cook both chometz and pesachdig at the same time. Best is to change over completely before doing major pesach cooking. We BH have a pesach kitchen but even so my wife only begins cooking a day or two before pesach – she likes fresh food!
Pesach cleaning: RULE #1. If you have been blessed with young children, believe me there is no such thing as ‘oh there probably is no chametz in there’. Forget it. Chametz is found on a constant basis in the most unimaginable of places. RULE #2 Crumbs are not chametz. Dont give yourself unnecessary work if it means missing out in the end by not managing things that are necessary or that make a difference.