Depth would have varied depending upon number of men in the army and the frontage needing to be covered. This is true of both armies. If you know the frontage to be covered and the number of men in the army, you can calculate the approximate depth of the formation.
No one knows exactly what form svínfylking took. The word occurs only twice as a noun and five times as a verb in Old Norse literature. None of these explain the formation. One of these examples describes the Anglo-Saxon army at Hastings forming svínfylking. Saxo explains it but is not reliable as a source and may be trying to give the Danes of the past links to the classical past. It certainly sounds like he is describing a Roman army.
Yes, Viking commanders would have stood near their banners with their best troops (huskarls) round them. Anglo-Saxon commanders would have done the same.
What do you mean by a ‘Viking circular shield-wall’?
Also, where are you getting your numbers for these formations from?