> að byggja landið ef þeir mættu það
> to settle in the land if they were able.

That's right.

> heilu og höldnu
> safe and sound

Yes.

> griðung einn
> one (?particular) Bull

"(this) one bull", "a bull"

> Þá urðu þeir varir við Skrælingja og fór þar úr skógi fram mikill

flokkur manna.

> then they were wary/anxious of the Skraelings and went out (only) in

large numbers (You'll never walk alone)

I think this is all the one event that it's describing, one particular
occasion: "Then [one day] they [the Norsemen] became aware of
Skraelings [Skrælingja, acc.], and there came forth out of the wood a
great host of men [i.e. the Skraelings]."

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

"fled with their burdens" (see my comments on Grace's translation).
Sometimes it pays to cheat and look ahead to the next paragraph (where
they still have their burdens)!