"Augustine moves to England in 597 and takes up residence in Kent. Eventually he became first bishop of Canterbury." Can I start with the present simple and go on with the past simple? Does first bishop take the definite article?
To me it would sound awkward. You should stick to one tense so tell the story either in the past or present - using present simple would make it more alive, add more action/interest to it.
Actually, he became the first Archbishop of Canterbury. (Wikipedia)