This is a pivotal issue in the series, and not just because of the big reveal at the end, but because many plot threads hinted at in the first three installments finally all connected into a nice pattern.
The visions and premonitions that came true
The Magic Memory Water was used to its proper purpose - as Willow used it first to clear the fog of artificial happiness that the super-coven magical 'opium den' put her under. She then offered it to Marrack - who declined the clarity of mind for the second time - only to turn out to be Willow's former teacher in the Dark Arts Rack. Finally she drunk from the flask again and recalled the word of the zen Caterpillar man.
The vision of somebody who used to be Willow's teacher 'at the end of times', and who turned out to be the exact opposite of Giles was fulfilled. I am glad it happened , but maybe a little not sure that it was needed. The strawberry plant on the #4 cover was a dead giveaway - especially when combined with Willow flashback to her scene with Rack in #1. But in any case - the Goddesses Gem vision was that of Rack, and I suppose its significance will be fully revealed in #5, after Willow's final confrontation with her former teacher of dark arts.
Finally, the zen caterpillar hints at 'Light and Darkness not being easily disentangled' and the Sea Anemone vision - the 'even my dark side...' part of it, were nicely tied up with the scene of confronting oneself Darker Side in the Liminal Planes.
Now as to character interactions.
Willow and Saga Vasuki.
I have to say that this installment ( and the recent snowstorm) finally pushed me into re-reading the entire TOYL arc of S8, as well as issues 10, 32, 32.5 - which were all written by Joss Whedon himself and , by the way , are a great read, even out of the context of S8. I find it is remarkable that almost all of Saga Vasuki's appearances in S8 were written by Joss. In fact her only other scenes in S8 are the brief cameo in WatG - she is appearing in a vision sent via vampire witch Kumiko Ishihara, and the 'clandestine conversation' in 37 - that was supposed to be written by Joss himself but was at the last moment reassigned to Allie, because Joss was too busy with Avengers.
In any case, I was checking on the logic of my reasoning that explains the TOYL appearance of FDW and her arranged suicide 'by Buffy'. So far my explanation holds - although we have to yet find the reason for the Fray future to be the 'good' desirable outcome for pre-Twilight Earth.
But as far as issue 4 goes, Aluwyn finally admits to 'Trying to restore something I'd lost too, but my way of doing it was as doomed as yours. I could not fix the problem, so I tried to cover it with something wonderful and beautiful '. This potentially means that she is aware of what is coming next - because for her it has already happened.
She then concludes her lament with somewhat touching and wistful : 'You must save your world. When you have, we can together again. To see if that's the end of our quest... or another stop on the road.' Which is just vague enough not to promise any kind of final resolution - meaning the snake-lady is not yet certain of where all of this leads - even if she already knows something that came before.
I always assumed that all through S8 Aluwyn was acting on behalf of Future Willow - who somehow managed to contact her in her then present timeline from the future. At some point it was a popular theory (which I back then found plausible) that Aluwyn herself existed outside temporal limitations - with past, present and future existing at the same time for her, while she was able to traverse time as a separate dimension. Willow miniseries make this theory highly improbable, so likely Saga Vasuki only knows as much as Future Willow has told her - which likely only what she needed to do : sent a message with magical signature via Kumiko, then make sure Willow and Buffy arrive in NY at approximate time of the temporal anomaly that would open portal to the future, then keep mum with present time Willow about what's to come - like Buffy's exchange for a demon and then Buffy's extraction. The only thing Aluwyn allowed herself to do was insist that Willow 'does not look', thus there was still a hope that Buffy will never tell present time Willow about killing her future self. We all know that did not work, because Buffy spilled the beans in the Retreat arc, after seeing Willow powerless and thus assuming her strategy of 'losing power' worked and prevented the FDW.
In the final exchange with Willow in #4 Aluwyn promises to 'be there however I can. As a guide, or whatever else you need.' Willow though, seems to give her favorite snake a cold shoulder, by insisting that she needs somebody 'who wants ( restore magic to Earth) as badly as I do.' To which Aluwyn only answers 'I know'. This making me feel puzzled again at how much of the future does Aluwyn know? She clearly know Willow will take Marrack as her companion - but it is not certain if Aluwyn will be back in Willow's confidants any time soon.
Overall though, I find that Parker/Gage's Aluwyn less of a trickster and mystery than Joss' Aluwyn. This snake goddess is more of a worried lover and an allegory of Willow's love of magic ( and power). Not to say I like her less this season - if anything Joss' Aluwyn was too alien to be likeable. This one is more intimate, and even her bad deeds are presented as tricks of a desperate girlfriend , not to say that these are utterly forgivable.
Willow and Marrack
There is not much to add to the already widely discussed reveal of #4. Sure, the clues of strawberry plant and Rack's vision back in #1 proved to be on target - the destitute warlock who was assumed to be dead turned out just disfigured into a nasty looking man-beast. He went a-walking in alternative planes , looking for raw power and magical ingredients , and got stuck there when the Earth was cut off. Of course it was Willow's 'luck' to run into him, then again nothing that happens in magical dimensions is accidental. Perhaps he wished for this particular meeting badly enough to draw Willow to himself - same as Aluwyn's tempering with Willow's divination spell brought Willow to herself.
Issue 4 gives us Marrack bursting with dark magic of the nightmare birds he consumed while waiting for Willow. So, when they finally come to blows over his discovered identity - he has a lot of dark power to swing about. I dare to predict though, that in the power struggle between these two it is Rack who is going to be sucked dry of all his powers again, thus Willow would likely have her fill of dark magic, to top her already charged ' light magic' battery. It is interesting to see if indeed 'energy is released by opposing forces', and how, and what for this energy is going to be released in the last issue of the series.
Willow considering to become the Seed
I am not really sure what to make of this development. I think the idea of Willow literally becoming 'the Seed' was floating around as a speculation since the end of S8. After issue 4 this theory got some solid ground. Willow finally admits that on one occasion Aluwyn truly was not tricking her - there is no way to nurture magic from the outside - if the world in question has no anchoring point. Thus she considers becoming the anchoring point that could be used to access out world from without and bring in a flow of magic. This potential development is especially credible in lieu of Willow reconciling with the idea of embracing her darker side - as a part of her magical personality. Because a potential Seed needs all aspects of magic to be hale, not just the light ones. This also goes well with Joss' Goddesses and Monsters pitch - about Chaos and Order embracing like loves, and with zen caterpillar's 'Light and Dark not easily disentangled'. I am quite puzzled over the fact that Willow series seems to be going in this direction - i.e. swerving away from the Manichean dichotomy - while at the same time the A&F series seem to have taken a path of enforcing the message of Big Bad evil being confronted by the Big Good as represented by Angel's Go Go team of him, Faith and Alasdair Coames. Well, you never know how it is all going to play out in the end. Personally, I prefer gran Edna's 'We cannot escape the dark, but we can refuse to let it own us.'