Your go-to secondary source on the Anglo-Saxons should always be Frank Stenton's exhaustive The Anglo-Saxons. For a book that in part is coming up on 80 years old, it's remarkably prescient. Obviously, do temper some of its more nuanced points with more modern reading. Higham and Ryan's The Anglo-Saxon World is a good start.

The Angles, Saxons and Jutes first arrive in the late 5th and early 6th centuries to serve as foederati in essence to Romano-British authorities struggling to cope with renewed raids following a series of particularly virulent plagues. Contemporary historians such as Gildas and Procopius present a long history of betrayal and ethnic cleansing, in which they usurp power and begin eradicating the British, but this has long been challenged. Debate has ranged from saying that there was just a small, elite invasion to there being no invasion at all, but evidence suggests that there was a relatively slow, drawn-out process of 'Germanification' across at least a century, with Anglo-Saxon language, material culture and political control slowly spreading West across the British Isles. With that in mind, there is still some evidence of Brythonic sub-kingdoms operating within a wider Anglo-Saxon hegemony as late as the 9th Century.

The first Anglo-Saxon king to convert to Christianity was Æthelberht of Kent, following the Augustinian mission of 597. Æthelberht's wife, Berga, was a Frankish princess who had long exerted pressure on her husband to convert. Æthelberht had largely resisted, as accepting Bertha's father as his godfather at baptism would have carried an inherent political submission to Francia. Converting directly to the papal mission allowed Æthelberht to receive the benefits of Christianity - bureaucracy, literacy, hierarchy, pan-European kinship and spousal approval - but still maintain his appearance of political autonomy.