I have some issues with Astarion's story. If Astarion was just abducted, why is there already a hunter 3 stone throws away from the crash site looking for him? It is not like anyone knew where the ship was going to crash. I realize a party might rest 14 times/2 weeks before getting to the tea house... but they might also walk directly there without a single long rest. So ultimately, I think this needs to be fixed. Feel free to ignore or use the suggestions below, but please fix this.
Suppose Cas occasionally toyed with Astarion by allowing him to escape and sent hunters after him. So what actually happened was Astarion was in the middle of one of these cat and mouse games when he was abducted. Thus... the hunters were already engaged when he was taken and knew to look for the a ship, etc... This minor tweak to his story would help explain why a hunter showed up so quckly if you want to leave things mostly the way they are. You could even hear about it from the hunter himself.
Have the hunter show up in camp one day as a camp event (similar to Rapheal), but only after a minimum number of rests. He could still talk about looking for a monster and going to seek the advice of a hag. But the long rests ensure he didn't magically appear an hour after the ship went down.
If you go with the first suggestion, you could also have Astarion's hunter abducted and aboard the ship. IE: His hunter is one of the companion options. So for most players, they have to choose between Astarion and his Hunter.Personally, I think they should fight when they meet forcing you to chose one over the other when playing someone else (less banter to have to record). But if the budget was there, I'm sure others would love the drama having both would bring to the party. I would also swap Astarion and this hunter's positions (Astarion at hags layer) so most new players will meet the hunter first and already know what Astarion is when they meet him. Even if they skip the hunter, they will know from that first parasite connection when they meet. So either way, the player knows immediately that Astarion is a Vampire without the whole not-so-surprising revelation. This would help eliminate so many of Astarion's conversation timing bugs.
Have the hunter/ranger be some badass true neutral or neutral good female that has hunted down Astarion several times before. If you choose to play her origin story she can have a conflicted relationship with the person she is supposed to hunt (and of coarse the ability to betray him by later turning him over to Cas). Conversely, if you play Astarion, a possible relationship with the "Gur" that Cas always sends to subdue you. Astarion would also have the option to betray her later by turning her into his thrall, assuming he eventually bites Cas and becomes a true vampire. Why a female? Because right now I don't like either of the other females. (Yes, I know it is a selfish request). Maybe Patch3 will change my opinion.