A question about going first while being rightmost on the turn order track.
When purchasing gems and building does everyone perform a single transaction starting with the start player and going around until everyone is done like the buy phase or does the start player perform all of their transactions before it goes to the next person?
I've assumed that all gem purchasing (phase 4) is done as one transaction. The rules don't say otherwise, but they do make clear that the gem supply cannot run out. Anyway, there seems little point in going around the table one set at a time: the chances of having some meaningful options for your second purchase are pretty slender.
The (English) rules say that in the build phase (phase 5), players in track order place one tile or pass their turn, and once passed can place no more. The tile purchase is a part of the placement transaction.