First I want to thank all the people who have provided the valuable information in this thread. I am a total newbie to using miles to upgrade across airlines. I have read through all the posts in this thread because I also would like to book an economy ticket on EVA to fly JFK-TPE-JFK and then use MileagePlus miles to upgrade that to business. If I may summarize what I've gathered from this thread:

1. First check the UA website award travel search, and look for desired EVA flights to confirm there are class I or Z availability for using miles to buy business class seats.
2. Go to EVA website to buy class Y or B seats for those exact flights
3. Go to UA SAUA website to request the upgrade with miles

I hope that is correct. I do have a few questions I hope you experts can answer:

1. I can't seem to search for specific fare classes on EVA's website. I can just select Economy and then see a bunch of different economy options. Do I just try to click on every single fare options that pop out to confirm the class code? Or is there an easier way?

2. Is there a consensus on whether I should look for class I or Z when I look on UA's website?

3. There are many references to ExpertFlyer. I checked the website and I think a subscription fee is required to access fare class information. Do most members here subscribe to it because it is worthwhile? Since I don't fly that much I didn't think $5/month seems worth it. But many of you seemed to want to confirm the class I/Z availability on both the UA site and the ExpertFlyer site. I also just read from ThePointsGuy website that UA and *A pulled their award availability data from ExpertFlyer. Any advice?

3. There were some disagreement about how far in advance one can upgrade the ticket. There were several reports that said the award availability is only open 2 weeks before the flight. But the most recent post said 331 days ahead was fine. I suppose early is better?

Thanks in advance for any advice you can provide. This is a great resource.