So based on what I've read, I can use Avios points to book U.S. (Portland Oregon is 2560 miles so redeeming in the 2,000-3,000 mile pricing) To Maui on Alaska Airlines for 12,500 Avios each, but can only do this by calling. I can convert some American Express rewards points to Avios during their bonus promotion 300:250 so about 42,000 American Express reward points would get me 50,000 Avios points needed for two round trips.

1) I've read taxes on British airways redeemed Avios point flights is very expensive (as I learned when trying to look at redeeming Alaska airline miles fromU.S. To Europe - varies but over $300 one way on one search), so how much are the taxes using Avios points to book PDX-OGG (Portland, Oregon to Maui) on Alaska airlines
2) how do I know availability of flight redemption to Maui if I have to call for redemption, but haven't converted to Avios points yet, let alone I'm not even signed up for British airways Avios yet. I'd hate to convert to Avios points and then find out no availability. Do I really have to call? So no online way to redeem Avios points for an Alaska airline redemption Oregon to Maui?
3) how far in advance can one book flights Oregon to Maui using Avios point on British Airways?
4) what are other's experiences on general availability of using Avios points on Alaska airlines for flights from Oregon to Maui?