I'm confused about the ideal world. Reading EvilGenius' translation for Guts talk with Flora, it seemed that the ideal world contained the soul.
I wouldn't rely on those translations dude, you'll get no love bringing them up here. And I really don't think EG even translated anything from vol 24. That was The Hawks. Even worse... It'd also help if you were more specific than just "the ideal world contained the soul". That's a little vague... Schierke calls the Ideal world the origin of all existence. But... you're really asking about some heavy-duty stuff that's hard to grasp for those new to the series. So buckle up, scanlation readers!

Within the Ideal World is the Vortex of Souls -- the giant whirlpool which Puck senses as a massive collection of evil. We see it in volume 3, 11 (within Wyald), 24, and now here, within Ganishka. The conglomeration of bodies that snatches away the souls of apostles can be considered an appendage of that vortex, or even just one of the tendrils within it. If you look carefully in volume 3, you can see that the swirls of the vortex are all composed of tortured souls. If you want to bring in Ep 83 into the mix, the Idea of Evil refers to it as an ocean of feelings, the dark side of humanity's collective consciousness. Later, it wraps portions of the Vortex around Griffith, beginning the process of Femto's creation. So it's got many erm... functions.
But is the Ideal World
just the Vortex? I lean towards no, there's more to it. But it's all that we've seen, aside from the Abyss, which is likely at the other end of the Vortex -- the dark place we see at the end of Ep 82 and in vol 24. But, we just don't know.
Have we seen any interaction between the ideal world and the physical world like the interaction between the astral/spiritual world and the physical world? Is there any good speculation on what the interaction between the astral world and the ideal world would look like?
I think you have the beginnings of a misunderstanding about the borders between worlds and the ah ... interaction between them. Flora and Schierke describe the world in a metaphor as if it's a massive ocean. In the "shallow" portion (or the surface, you could say), is the physical world and all its inhabitants. As you get "deeper", the surroundings become strange and filled with otherworldly beings. Deeper and deeper is where you come to the massive beings that we know little about, including the Ideal World.
From an objective view, the astral world's layers are divided by gradual shifts. But regular humans would encounter a so-called locked gate in deeper portions as they're limited by their perception. Flora says magicians are able to transcend those boundaries by releasing their spirits. But another good example of how the worlds interact for those who can traverse them is how Guts and Co. stumble into Flora's mansion. Guts and Casca exist at the border between the Astral and Physical. With the band, they went from established places in the physical world, through the deep woods, into somewhere completely different and deeply tied to the astral world. This was only possible because they're branded, of course. They're no magicians

But no, to answer your question in a roundabout, the Ideal World doesn't come into contact with the Physical World like this naturally, because they're separated by that massive difference of depth. This is a completely unique phenomena we're witnessing, and likely the most all-encompassing change the Berserk world has ever gone through, short of its creation.
I touched on this next point during the above post, but I've been thinking about it tonight, and there may be a very easy explanation, or it may be something we haven't considered yet. First, lets take a look at these two images.

We're all familiar enough with this one by now. The vortex is inside Ganishka.

But the Vortex was also inside Wyald, pulling him down into "hell."
From the "deaths" of the chibi-Ganishkas surrounding him on pages 12-13, it's clear Ganishka has died. But is the apperance of the Vortex in 304 simply part of the natural deconstruction of Ganishka's apostle form? Or was it there, as we have been discussing, because of SK's intervention in slicing the rift between worlds. Either way, something unforeseen happens in 304 with the light emitting FROM Ganishka. I just don't know yet what the implications are, along with the appearance of the Vortex. I honestly think we're going to have to see the effects of this transformation of the world before we can deduce exactly what's happened.