It’s not nearly as bad as it may seem. While it’s difficult to build a one-way itinerary by hand, assembling individual flights that don’t appear if you try searching from your origin to your destination, it should be no problem at all to book a multi-city trip provided that (a) the origin and destination for each leg show up when searched as a one-way and (b) you’re not doing anything that an agent might consider abusing the spirit of the rule. The website simply has some issues with large multi-city searches.

Also, from what I can see, it looks like you’re booking in business class? The only reason you’d need to worry about Priority Pass is for domestic club access on connecting flights. In most cases, a Priority Pass lounge is going to be no better than the one you’re able to access as a Buiness Class customer.

For example, on the itinerary you listed, assuming everything is ticketed in Business Class, you’d have access to the Lufthansa Business lounge at DTW, the Polaris lounge at SFO, one of the EVA lounges at TPE, and the Royal Orchid lounges at BKK. In fact, I’d look for a longer layover at BKK personally, because otherwise I don’t think you have time for the free* massage at the spa.

Yep, this is absolutely a valid excursionist perk segment.

If you have no flexibility at all, you might want to scoop up the award space as soon as it arrives, with the understanding that you may not be able to get the Excursionist Perk. If you have some flexibility — for example, if you’re willing to add a connection somewhere — you can probably roll the dice and get it on a single award. I’ve yet to run into any occasion where I couldn’t find something; it might just not be optimal.

* gratuities welcome