This answer is largely based on the Movies & TV post which user1964 linked in a comment.
Yes, Poirot was a religious Catholic.
In the story Murder in Mesopotamia (Internet Archive link), he mentions twice that he is a "practising Catholic":
Then he said quite irrelevantly: ‘An interesting man, that Father Lavigny.’
‘A monk being an ...
TL;DR: It is not possible to put together a consistent biography of Poirot that includes all the stories.
Precise dates are very rare in the Poirot corpus, and there are few references to historical events that can be used to give a terminus post quem, but here is a selection of significant dates.
“I had a bad failure in Belgium in 1893. You ...
Hercules Poirot was born in Belgium, between 1875 and 1880 … or before. He entered the Belgian police when 18 years old, between 1893 and 1898. He retired from the Belgian police with 22 years of service, between 1915 and 1918. He arrived in England between 1916 and 1918, because the First World War was ending.
His first case was The Mystery of Styles in ...