> og buðu þeim og vildu vopn helst fyrir
> and offered them and wanted weapons rather preferably

"and offered them and wanted weapons most of all in return"

> en Karlsefni og förunautar hans höfðu eftir bagga þeirra og

skinnavöru. Fóru þeir við svo búið í burt.

> but Karlsefni and his fellow travelers had their packs and skin

wares back (in return). They went away as it happened?

"but K. and his comrades were left with their packs and skin wares.
They went away with matters thus."

'við svá búit' "with matters thus", "with things as they stood", "with
the situation thus", "this being the situation".

Otherwise, your translation looks good to me.