I agree with Mary Newberry, born 6 Feb 1795, baptised 9 Mar 1803, daughter of David and Elizabeth. She was baptised as part of a job lot of four Newberrys, and appears in censuses as born Arlesey with the right age. Does the marriage entry at Studham say "Mary of Arlesey? Not that I'd be too worried if it doesn't, given the census evidence. It begs the question as to what happened to their daughter Mary baptised 7 Sept 1785, as I can't find a burial; nor can I see what they were doing between 1790 when their son John was baptised and 1795 when Mary was born. But Hannah's birth is given as 8 March 1798, whereas she's shown in 1841 as aged 36, and as she appears to have died before 1851 there's no second bite at the cherry. How have you established that Hannah Martyr was the sister of Mary?
I'm assuming that it was this David who was buried in Arlesey on 12 Nov 1816 aged 59. Which gives a birth year of c1757, tying up neatly with the baptism in 1757 of David Monk or Newbery, son of Joseph and Arabella, who also baptised Mary Monk or Newbery in 1750 and Joseph Newberry alias Monk in 1736.
These are the first Monks or Newberrys in Arlesey and there's no extra detail in the 1733 Ickleford marriage. I'm still looking at possibilities, and where the Monk may have come from.
I don't take much notice of other peoples' trees, other than to get ideas. Look at the six on Ancestry - all have a Sarah born 1827 at Arlesey, daughter of Joseph and Arabella. There's no such baptism at Arlesey, and according to the birth dates Joseph and Arabella would both have been 13 at the time, 6 years before their marriage. It looks as though they've all copied each other!
I think your line looks right, my only query being what happened to Mary baptised 1785.
I'll get back to you on the Monk aspect
David