> er þann sið bjóða
> and preach their faith

More specifically: "who preach that faith"

> and landed at Gautavik
> þar sem heitir Gautavík

A reasonable paraphrase. MM & HP, also paraphrasing a bit, have "at a
place called Gautavik".

> greifa
> Count (greifa - like the German - Graf)

That's right (and compare the English loans from German: landgrave,
margrave, palsgrave). The nominative singular of the Old Norse word is
'greifi'. The Oxford English Dictionary has an entry 'grave' n.3.

"[a. ON. greife, of obscure origin; prob. a. OS. *grébio (MLG. grêve)
= G. graf GRAVE n.4 (In South Yorkshire documents of the 16th c.
GRIEVE n. and grave are used indifferently.)]

"a. A steward, a person placed in charge of property (obs.).

"b. In certain parts of Yorkshire and Lincolnshire, each of a number
of administrative officials formerly elected by the inhabitants of a
township."

'grieve' (from Old Northumbrian 'geræ´fa') is a northern form of
'reeve' (Old English 'geréfa', earlier 'giræ´fa', hence sheriff =
"shire" + "reeve"), "of uncertain etym[ology]" says the OED,
"app[arently] not in any way related to the continental forms cited
under GRAF, GRAVE n.3 and n.4."