'gestahöfðingi'. Chief of Guests seems to be a bit of a euphemism.
MM & HP: "The leader of the King's Spies". They have a note: "The
King's Spies 'gestasveit' were certain members of the kings retinue
whose function was to look after the internal security of the kingdom.
They roamed the country seeking signs of incipient rebellion and
getting rid of trouble-makers - a sort of medieval F.B.I."

> Vel er þar til fengið

MM & HP: "That is generous."

> Farist þér nú vel.
> Go (you) now well.' (Farewell, Have a good journey!)

More literally maybe: "may it go (turn out) well for/with you."

> Gautlandi hinu eystra

MM & HP: "East Gotaland", i.e. modern Swedish 'Östergötland', part of
the southern Swedish mainland, rather than the eastern part of the
Baltic island of Gotland. I suppose there's a few possibilities for
anglicising the name while avoiding ambiguity; another would be just
to half translate the Old Norse version: East Gautland.

> í Leginum

ON lögr (MnIc. lögur), dat.sg. legi + the definite article. "The
Water" = Lake Mälaren near Stockholm (not Vänern, which is further
east) [ http://en.wikipedia.org/wiki/M%C3%A4laren ]. Declined like
'völlr' "plain, field", dat.sg. 'velli'.

> úr Jamtalandi

Modern Swedish district of Jämtland.

> Stokkssund

Swedish 'Stocksund'.