My apologies for not replying before now, I've been horribly busy and on the two occasions I tried to reply the Ancestry site was down for hours!
I'm actually really overwhelmed with all you've found out. I would love to be in your position of being able to look through all the original documents and make the transcriptions. The Internet doesn't compare at all.
However, I do suspect that the Lettice Hooper burial you found from 1823 might not be the right Lettice, because being 62 then would have made her 47 for the birth/christening of the last child, William, and that's rather old for those times. Charles was born in 1776 so would have made him only 47 himself in 1823, and that's a considerable age gap. There's also no indication that the family lived anywhere other than Milford. So, reluctantly, I think it must be another Lettice.
What I have realised from your info: Charles and Mary were married in November 1832 and their eldest daughter Ellen was baptized only three months later - so clearly there was a very urgent need for a marriage!
I do wonder if it was our Charles who had a second marriage to Martha Guisler, between Lettice and Mary. It wouldn't surprise me one jot.
Unfortunately I don't have too much time for research this week, but I'll order a few certificates (they take a month to get here) and will get back to you once I've absorbed the info more.
I've also shared this info with my Charles Hooper mutual ancestor (he is the 3x GGF for both of us) and she has come up with a lovely link: it turns out Charles and Mary were witnesses to a manslaughter in 1837 when Sophia Wilcock accidentally killed her mother-in-law - the Wilcock family later settled in Pembroke Dock and her husband William seems not to have been too offended that his wife killed his mother, as they went on to have lots more children! Weird thing, families!
Thanks again, and look after yourself, Nicola