Hmmm. While the Far Realm things can easily be a an over-arching heroic plot, you've got epic fairly tightly packed. Imix, Ogermouch, Torog, and Lolth are all competing for "Campaign Ending Big Bad" space. Granted, you can do Imix vs. Party at level 28, Ogermouch at 29, and have Lolth revealed as the Man... Woman... Spider-thing behind the Men this whole time for a big epic brawl at 30. Torog would be hard to fit in though, and competes with Ogermouch for a place at the table as far as "Adventuring Ending Solo Fights" go. Course, you can delevel or boost these figures to your liking.
Perhaps heroic could start out simple enough, with the party dealing with a simple Village vs. Generic Evil Race plot... at least until the chief Orc's head explodes Resident Evil 4 style into a bushel of flailing barbed tentacles. As the PCs move past this point they come to across more and more chaos being spread, all with the faint touch of the Far Realm. Eventually they learn that these events are not so chaotic, and all being contrived by a single mad mastermind. Tiresias is a powerful warlock lording over a cabal of heretic mind-flayers, foul-spawn, and cultists. He is guiding his cabal to some greater purpose, driven by his visions of the future. Eventually it becomes revealed that these sights of bloodshed are forming a ritual circle concurrent with celestial formations, and, given a months time, the ritual will go off creating a planar overlay with the far realm using the life force of a thriving city which will be sacrificed when the lifeforce goes off. As the party tries to thwart Tiresias they learn that, as mad as he appears, he is quiet sane. He turns out, is a nobleman, a powerful duke and cousin of the reigning king. He's not even truely a prophet, but merely spouts predictions, and then uses his money and public persona to make them come true at a later date. Insane people while dangerous in the short term, rarely have the power and insight to plot long range. Without Tiresias's reasources and plans, the various lunatics under him employ would be minor threats at best.
The king is an unpopular one, made more so by the chaos Tiresias is causing. Once the city is lost and the far realm abominations are set loose, the king's hold on the throne will most likely collapse. Most of the cultist will die as part of the ritual, and while dangers, the abominations are mostly mindless and easy to wipe out with an army. Even then, the destruction such an event will be massive. Tiresias will step up as legitimate contender for the throne, and is already planning to capitalize on the disaster and the already hefty distrust of mages by the populace to build a strong propaganda base for his regime. Once secure he will have the throne he felt cheated from decades ago.
Tiresias is a cunning foe if nothing else. If the players try to expose him, he has enough political pull to silence them. Furthermore, he can use legitimate forces against them as well, forcing them not only to deal with the machinations of his lunatic pets, but also things like local paladins and the city guard, forcing the PCs to become outlaws. He also has a powerful servant in the form of a Drow Warlock and advisor who is his confident in all things and is a powerful foe in her own right. If the PCs manage to break his cabal though, he may try and set the ritual off early with disasterous results. While the gate will open, it will be an unstable one. Charged with the waning energy of the Far Realm he may attempt to combat the PCs head on and try and wipe them out, and then use whatever chaos the ritual causes to move ahead with his plans. In the end, if the PCs win, the magic back fires and he himself is pulled screaming into the Far Realm while the magic of the flawed ritual causes the whole city to break and sink into the Underdark.
This scenario gives you an interesting basis for a powerful villain. He's smart, savy, and intelligent. With his Drow advisor and the suken city, it also gives you a straight path into the Underdark for Paragon onward. Also, there is a change Tiresias can become a reoccurring villain, returning later as a powerful Far Realm entity and shapeshifter, still seeking the throne in the chaos caused by his failed schemes.
Perhaps Lolth had her servant help the nobleman to help cause chaos. Perhaps her ultimate goal in the campaign is to sow discord among the world and the gods to get after some coveted prize, and pety but dangerous mortals like Tiresias are merely a first step towards cosmic calamity. Perhaps in Paragon the servants of Torog will begin assaulting the surface using the fallout of Tiresias's mad scheme as a stepping stone, and she can manipulate the PCs into finding her an artifact to help her to kill Torog, giving her sole control of the Underdark. Then in epic she can trick Imix and Ogermouch in the guise of an agent of the Elder Elemental Eye into creating a global erruption which only frays the fragile nature of reality in the deep Underdark and unleashing a massive and apocalyptic Far Realm incursion, during the chaos of which she begins to hunt down Gods and Goddesses who have wronger her and slay them. In each stage her influence becomes more and more pronounced until finally the PCs must confront her, Ogermouch, and Imix deep within the Elemental Chaos and slay her before she brings the whole universe down around them.
This might be a little more than you asked for, but I hope at least some of it helps.
