Not too much trouble with the last one, I see.

> "[...] eða hvað vilt þú fleira til mín tala?"
> Snorri mælti: "Það að (seems redundant?) mér þykir þú maður

harðlegur og mikilfenglegur

`það' is in reply to Skarphéðinn's question:

"[...] but what else do you want to tell me?"
Snorri said, "That I think you a hard and formidable/stout-looking man
[...]"

> þá skuld eiga allir að gjalda

"THAT debt, all have to pay" (i.e. everyone must die). Rather than
"THEN all have to pay a debt".

> þar [...] er þú situr fyrir

"where you're sitting", "where you're sat". To be literal, we could
translate `fyrir' as "before [me]" or "present", but it would probably
be left out, in this instance, in idiomatic English. MM & HP take the
relative particles as indefinite: "I would dare face you anywhere."