Hello.
I don't know how are you going to move there, by car, by bus ...?.
Personally, I would choose your second option "2 nights north (LaCoruna?), 3 nights Santiago, and 2 nights south (Pontevedra / Vigo)?" and, between Pontevedra and Vigo, I'd choose Pontevedra (but moving me a day to Vigo).
Last summer I was in Galicia and the best views I saw was in Vigo. There is a huge bridge at the entrance of Vigo and the views from there were really amazing (in my opinion)
. But, I went by car and I don't know if it is easy to go to that bridge by train, bus, etc. Maybe Eddie has more information about this.
The second place I liked best, was a little village called Tuy, but I think is too far from Vigo, just in the frontier with Portugal.
Too many good places to see there
, and too few days to stay
Bye!