I think your research will be well worth it as I do not know of any prior published research regarding the Masterman family.
I myself do not hold the Masterman surname.
My ancestry is as follows:
One of my great grandfather's was Walter Masterman (1880-1971), he was the only son of the marriage between Levi Masterman (1835-) and the widowed Pharasilow (Young) Knowles (1840-1928). Levi had a previous marriage with Celestia Doble and had two daughters before the marriage ended (either officially or unofficially) as she remarried to Holland Newman prior to the marriage between Levi and Pharasilow.
Levi was the son of Daniel Masterman (1794-1878) and Eliza (Betsy) Storer (1798-1878).
Daniel was son of James Masterman (1759-1842), the same as your James, son of Marmaduke.
So, Captain Marmaduke Masterman was my great5 grandfather.