See, the Grey Jedi thing makes me want to copyright or trademark our stuff. Seriously. So help me if I see our characters used without our permission in a "canon" book or film...xD

Cause lets be real here: we've built an entire alternative universe BASED on the idea of the Force not being light and dark. We were doing this before Disney was! *shakes fist at "the man"*

Anywho, to your thoughts: 
-Makes sense on all fronts in your first point. This would more than likely take them DEEP into Wild Space, though. Even deeper than our duo went to discover Renso. More worldbuilding it is, then! Might have to wrap up this third act and have an intermission of sorts to make sure we know where we're headed before we begin Act IV. 

-Hmmm...wouldn't be interesting if there was an entire section of the galaxy taken over by the Rakata? They're an ancient race that obviously had the technological means to crush the galaxy underfoot in KOTOR, but it seemed that their efforts were thwarted somehow. Don't remember if their sudden disappearance was really explored in the Old Republic universe, but I think it would be interesting to explore. 

Edit: As I finished that last sentence, I found an article on the Infinite Empire, which is exactly what I just mentioned. I'll include the link at  the end of the post, but basically the Rakata took over the now Alliance controlled sector of the galaxy and made it their empire. Their creations fed on Force energy, which led to the downfall of their empire, seeing as their own machinations fed on their energies. This could totally sync up with the creation of the True Sith(or Sith, I suppose), which rebelled against the abuse of the force and created their order from the ashes of the Infinite empire. Cue Renso and the founding of organized force users. 

SO, with all that said, here's what I'm thinking plot-wise for our next act for your perusal/modification: 

Manus wanted to find Revan to glean knowledge of Rakatan weaponry and tactics, to essentially feed off of the energy of others(sidenote: interesting how we created the Xiis, a sentient race that did the same thing...tie that in somehow?) and strengthen his "living weapon" philosophy. The Mystics were being forced to go back in time and find Revan, which they were obviously unsuccessful in doing, but upon entering into a deeper trance enhanced by the Force energies of the Force users at the meeting you set up, which results in the Mystics claiming they saw Revan and the Exile enter a ship and fly "into a void. A void they knew would end, but offer no return." They also see a massive structure floating in space, one that "destroys life, destroys harmony and energy". The mystics believe that the separate visions are tied somehow, but can't offer specifics. This leads to scouring of records on Voss-Ka and Zinuthra, the Qyaari connecting the dots between the Star Forge and Revan. Speculation abounds about there potentially being another Star Forge and a resurgence of Rakata. While seemingly impossible, the Elders agree that investigating this vision would be worthwhile. 

That's all I've got so far xD