Court activities, and the cheapest way to raise Infamy

After the prologue the main story is not a corridor. You anger the three vampiric vassals — Ambrus, Bakir and Xanthe — by disrupting their operations across the valley. Each disruption is a court activity, and each one raises Infamy. Reach maximum Infamy in Vale Sangora and the final quest opens up.

The order the boyars are meant to be fought

PowerPyx recommends Ambrus, then Bakir, then Xanthe, on level range rather than story reasons. Each has a quest attached — The Gilded Gauntlet, The Lunar Game and The Cycle of Love. Once all three are dealt with and Infamy is maxed, skipping time to the next day unlocks A Deal with the Devil, the final quest.

Any boyar you leave alive turns up as a boss inside the castle assault instead, so skipping one is a trade, not a saving.

Is it worth doing more than you need?

Only if you want them. Court activities are repeatable, so it is possible to spend a lot of budget here — 30 segments per full sweep — but Infamy caps out, and past that point you are paying for loot and XP rather than progress. Given that combat itself is free, grinding activities is one of the few genuinely wasteful things you can do with your time. The planner counts each activity once, so if you intend to run several, add 3 segments per extra run on top of what it shows before you commit to a sweep.