Unfortunately, the date of emigration is not certain. It's anywhere between 1851 and 1855, and I have not been able to find the family in the 1851 England census. That it something else to re-visit in my research, though. I know when he was naturalized, however, records are not organized in the town and they can't find his record. Yes, John's youngest was born in 1840 in Epsom. The others were not.
The baptism you found is definitely a possibility--thank you so much. Do you know if it was at St. Nicholas? He did marry there so it may be his family church.