> Hin sama var umræða á Vínlandsför sem fyrr
> At the same (time?) (there) was discussion about travel to Vinland

as before

"There was the same discussion about travel to Vinland as before". The
subject of the sentence 'hin sama umræða' has been split by the verb
'var'. Some more examples of split constituents:

'góðan eigum vér konung'
"we have a good king"
(Heimskringla: Óláfs saga helga 208)

'ok allr var hans líkami vel skapaðr'
"and his whole body was well formed"
(Sturlaugs saga starfssama 1)

'allir váru þeir frændr miklir menn ok sterkir'
"all those kinsmen were big men and strong"
(Hrómundar þáttr halta)

'miklu skal þat betra vera áðr en ek létta'
"it will be much better before I am finished"
(Þiðreks saga 67)

> og skáru hvalinn.
> and cut up the whale (nominative??).

Accusative (masculine).

NOM. hval(u)r + inn -> hval(u)rinn
ACC. hval + inn -> hvalinn

> Karlsefni lét fella viðu og telgja til skips síns
> Karlsefni had wood felled to cut for? his ship

Yes: K. had timber felled and carved/cut (shaped to fit) his ship.

> og lögðu undan með byrðar sínar
> and laid down with that their burdens

"and fled with their burdens" - see the next paragraph where they're
still carrying them! (Þá tóku Skrælingjar ofan bagga sína og leystu og
buðu þeim og vildu vopn helst fyrir en Karlsefni bannaði þeim að selja
vopnin.) And compare 'leggja á flótta' "to flee"; 'leggja eptir' "to
pursue" [ http://lexicon.ff.cuni.cz/png/oi_cleasbyvigfusson/b0379.png
(right column, top)].