I don't have notes on your particular Donahue family. I looked at all the New York "Michael Donahues" I could find in the U.S. census, and probably looked at your family and went on since they weren't the ones I was searching for.
It appears that your Michael Donahue must be Catholic, with his mother being named "Bridget," a very Catholic/Gaelic Irish female given name in honor of a saint, and Michael himself having a saint's name. Is that right? He was probably from what is now the Republic of Ireland, but Donahue surname variations are really common there and without an emmigration record/ship passenger list or other record where his exact place of origin might have been stated, it's difficult to identify his home location.
Do you know if your ancestor Bridget O. Donohue, born about 1813 Ireland, came to the U.S. after the 1840s (Michael's birth date in Ireland) and before the 1880 U.S. census with children and husband Frank Donohue, or did she emigrate late in life as a widow, perhaps to join her son Michael and his family already established in Westchester County? Makes a difference in what you might find on the family.
You wrote that "Michael [Donohue] died Sep 25 1990" but must have meant 1900, since Michael ("Martin Donohue") and wife Johanna and children were counted in the 1900 Westchester Co., New York census. His birth date as listed by the census taker as "May 1845" and he had emigrated to the U.S. in 1865 -- a good lead to follow in ship passengers lists for him alone, him with mother and siblings, etc. Wife Johanna (Christopher) was born "Mch 1853" and emigrated to U.S. in 1875 (1872?), another research line to follow if you haven't already done that.
You know you can use the "Irish Times" web site (as well as others) to check prevalence of ancestors' names in mid-1800s in Ireland. Their households index is taken from Griffith's Valuation 1848-1864.
You might have good luck checking further on Christophers in Waterford, since you know Johanna was born in Ireland in 1853. Her parents would have been residents there at the time of Griffith's Valuation. And, there were "Donohues" in Co. Waterford too. Maybe the Christophers and Donohues knew each other in the old country.
An index to Griffiths Valuation for all Irish counties and townlands is on this site:
My Irish families (Hadden, Campbell, etc.) were Ulster Scots Presbyterians and most of my research has involved Northern Ireland counties. I don't know "my" Michael Donahue's religion yet, but it would have been unusual for a Presbyterian like the widowed Mary Campbell to marry a Catholic in the mid-1800s, although not totally unheard of... so I'm thinking even with a Gaelic Irish name, my Michael was probably Presbyterian or another religion. There were Quakers, Methodists, Church of Ireland, etc., in Ireland in the 1800s.
If you want more references for Irish records databases, I'll be glad to share those I've marked as helpful. And if you've already explored all the things I've mentioned, at least you've done the most you could in your Irish search!