ok eru þar of vetrinn.
and _______ there on the way.
Again, this is an expression of time. And (they)
are there for the winter.
Þess er við getit,
There he went with
at Auðun kaupir þar
bjarndýri eitt,
to Audin to buy one beedrink, or to buy Audin some
mead.
This is tricky! Þess is the genitive singular of
þat meaning "of that"
er means is
við is a preposition which can have many meanings
according to the context. Here it is "about" or "concerning"
getit is the past participle from geta which can also
have a number of meanings, one of which is "to relate" or "tell of".
So, put altogether, this gives us
"It is said of this..." or "About this it is
related..."
at Auðun kaupir þar bjarndýri eitt
that Audun buys a bear
kaupir is the present subjunctive of kaupa to buy,
because this piece of information is related.
eitt is a numeral "one" - here in the neuter to agree
with bjarndýri.
gørsimi mikla,
______ much (or greater)
gørsimi is a feminine noun meaning "a treasure".
You are right that "mikla" means great and it takes that form to agree with the
feminine noun.
ok gaf fyrir alla eigu sína.
and gave for him one
Here we have that word "eiga" again, but here it isn´t
a verb, it is inflected "eigu" in the accusative form and as a noun it meaning
possessions.
sína is a reflexive pronouns agreeing with eigu and
refers back to the subject of the sentence, i.e. Audun.
So put that together and we get
and (he) gave all his possessions for
(it).
Ok nú of sumarit eptir fara þeir aptr til Nóregs, ok verða vel
reiðfara.
and now they traveled after them to Norway, and were well
traveled.
And now, the following summer, they travel back to
Norway and have a good journey.
"verða vel reiðfara" is a set phrase according to E V
Gordon.