All in all, I'm pretty pleased with how it turned out - it was a perfect fit as I used an existing sweater as a template. The only finishing to do once I'd completed the pattern was to graft the underarm stitches together using kitchener stitch (and darn in loose ends of course). This is a technique I'm well used to during my sock knitting so it stood me in good stead - I still follow written instructions for it though! It gives a lovely neat finish and it worked well - no lumpy, bulky underarm seams.
Love that this style of sweater is done entirely in the round and in one piece - I'd definitely make another one :)
If you're thinking of making a lopapeysa, I'd definitely recommend giving it a go - they're great fun and quite straightforward (you might need good arm and shoulder muscles though - they become quite heavy by the time you reach the neck shaping!)
See you soon!