What records exist to connect William to his parents as well as his marriage and many children? Most of the children's profiles are unsourced. William's profile is as well. I added a link to his profile at FamilySearch along with data on legal records from the FS site, but the records date to 1646 and his profile has him dying in 1625.
He has a dozen children attached to him that all need reviewing.
This site appears to be where the legal records mentioned on FS originated. It provides no sources for his parents or marriage and only lists seven children.
Ancestry.com. England, Select Births and Christenings, 1538-1975 [database on-line]. Provo, UT, USA: Ancestry.com Operations, Inc., 2014.
Seems quite common (wth variants)
Essex Record Office; Chelmsford, Essex, England; Essex Church of England Parish Registers