1) The only times I see the promo codes is when they have announced special sales, such as the New Year 72 hour sale they did last year (at least for people in the USA).
2) I definitely prefer the PE seats on the 777-300. If you can, get one of the middle two seats as this will ensure you have direct aisle access and not have anyone disturb you to get out. They market the two middle seats as being for couples and the two on the sides for solo travelers but I personally think it should be the other way around. Let the couples share one aisle access and let the solo travelers not be disturbed by strangers.
3) In LAX I believe you are limited to the choice of Koru Lounge and Air Canada. They are located next to each other so you can decide for yourself - I've never been in the AC lounge. I've only ever used NZ's lounge in Auckland, so I'm not much help there.
4) I can't definitively answer this one but my guess would be no.