I'm not sure how to trigger the quests on Harmonia. Unless I'm mistaken, the vampire and goblin quests were available to me the moment I got there, and then shortly after, the "beast" quest somehow got unlocked, though all of them can only be done once. If you're wondering how to farm money on Harmonia, the best way at the moment is probably just repeatedly doing the 50/100 gold cup thing at the goblin camp (and potentially stealing from them each night), it resets every day and crossing the valley progresses time fast.
Rather than being rejected by Feraldo, I meant that the game assumes you've rejected him if you landed on Harmonia first without talking to him on Akra, though I'm pretty sure you can still accept being his omega if you go to Akra afterwards and have that conversation. If you accept his advances in regards to being his omega, then instead of the dialogue you got, you can either state that you're okay with him "knocking up" Gabriel or you can be jealous (which he likes, amusingly). It's clear that there's going to be a separate path where the protag could dominate him and become his alpha, though given his overall nature and the way he naturally expresses affection (loves protecting/caring for the protagonist, etc), being his omega sounds much more romantic than dominating him imo. :p
I was being mildly vague to be less spoiler-y about Feraldo but it's nothing major.
Edit: The vampire quest and potentially other stuff might only be available in the current patreon version btw (which I'm playing with).