> hafður

You're right, here it's the past participle of `hefja', another
alternative besides `hafiðr' and the etymologically correct `hafinn'.
CV gives a few examples: `hafðr til ríkis', `upp hafðr', `önd hennar
var upp höfð yfir öll engla fylki'.

> og er þó nokkur vorkunn (várkunn) á

"but there's some excuse for [you],"

> þó að svo sé."

"even though it is so" (i.e. although it's the case that you've been
happier than now, there is nevertheless an excuse for it). The `þó að
svo sé' is redundant; it doesn't add to the meaning. It sounds a bit
odd in English, especially if it's left at the end of the sentence,
which is presumably why MM & HP avoid doing that. Just a stylistic
difference between the way the two languages express things, I suppose.

> mikla mína eigu
> a great (quantity of?) my possessions

That's right (Zoega 3).