Here's where it gets grim.
I thought I knew Sith, but this chunk of Rave's notes has details that I've never seen anywhere. It's an annotated account that claims to be about five millennia old. It's the sort of thing I'm going to keep locked up in a serious way. If even half of it is real, this kind of thing can't get out.
Point the first: either the Bodo Baas holocron has different filters than most, or we've fundamentally misunderstood how holocrons assess the readiness of their questioners. The Baas holocron gave him far too much information about the Sith; his Master, Vodo-Siosk Baas, had to shut it down. Was Kun still sufficiently Light, and already strong enough as an Apprentice, that he could access it at such a level? Either way, I'm glad @Seydon of Arda has the Baas holocron.
Less worrisome, but just as pressing, is the model of Jedi organization that the Order followed in those days. The Order had no central leadership per se; it was a network of small individual enclaves led by a few Masters, or even just one, with their students. Very much in the vein of ancient martial arts schools. In times of crisis, they'd gather for convocations; thousands of Jedi and hundreds of ships came to Deneba. I feel like this model comes close to describing the current state of the Jedi, and might be desirable. Worth closer examination, anyway.
Notes on Exar Kun versus the beskar walls of Freedon Nadd's tomb. At a standard setting, his sabre barely scratched them. When this ambitious but half-trained young Jedi dialed up his sabre's power setting, he cut a passageway through about a metre of beskar with ease.
Here's another thing that makes me wary. I can't release my notes on Rave's notes on this - but this is useful, very useful, to know. Ulic Qel-Droma's command ship was rammed by a Krath Chaos fighter, whose pilot was under a Sith spell of mind control. Ulic was injured, and that wound refused to heal, due to some otherwise unknown effect of Sith magic. Was it a spell Keto launched at the moment of impact? Was it some kind of efflux of the qazoi kyantuska or however you pronounce it? Either way, unhealing wounds at starship-scale ranges...that's frightening. Rave knew the standard Sith Magic sources cold, and she'd never heard of such a spell.
She had, however, been to a certain mausoleum on Korriban. It's a planet known for putting up mausolems to Sith Lords, but this one was specifically for fallen enemies. A tall spire of crystal, maybe eight or ten metres, held the souls of Jedi Masters who'd fought the Sith and failed. Nadd destroyed the crystal and released the spirits when they'd served their purpose. I can't help but see a parallel to Ruusan -- and a method of making a Force nexus that doesn't require a thought bomb. Ugly stuff. Adjacent to that mausoleum was another, much larger one, where many old Dark Lords rested, 'their bodies preserved by their own power.' Their leftover shades pronounced Kun ready to become a Sith after he called on the Dark Side to defeat tuk'ata guardians.
After Nadd healed Kun with Sith magic, Kun could read Sith runes without study. Previously, he'd used an electronic translator.
Here's where it gets worse. One of the Sith temples on Yavin Four contains a circular interior arena. Galleries around the wall could seat somewhere around ten or twenty thousand people. The Massassi would put up something like crucifixes intersected by circles, and more or less crucify dozens or hundreds of their own as part of a ritual. There was a chant, too. The temple would respect their sacrifice, Rave says, and the chant would cause pillars of fire around the perimeter of the chamber. The focus of the ritual was one of Naga Sadow's Sith amulets, carried by a high priest. Perhaps the ritual was meant to empower the amulet. At the centre of the chamber was a huge pit with a lid. The last time the ritual was performed, or probably the last, it awoke Naga Sadow's Sith wyrm, a critter the size of a capital ship. The wyrm came up from the central pit and started wreaking havoc. Exar Kun used the empowered amulet to destroy it a piece at a time, just shred it. Underneat, in the pit, was Sadow's old ship and alchemy apparatus. The main apparatus was in the shape of an inverted spike the size of a small corvette, and the being who was to be alchemized was strapped to it. Rave has a ton of notes here -- she duplicated the apparatus and improved on it, because of course she did.
The implications are pretty broad. I doubt anyone, even the Rekalis, knows that at least one of the temples has dormant power like that.
Also good to know: sith poison may suck when you're first dosed with it, but it doesn't truly kick in until you get seriously angry and use the Force. Then it hits, amplifies your anger like crazy, and makes you addicted to the Dark Side. I'll pass on the delayed-reaction information to some healers.
Another point, potentially a very dangerous point -- as if the other things I've found haven't been lethal -- is about amulets. Sith amulets have a whole other function. Ancient Dark Lords could use them to send tangible messages forward in time. Marka Ragnos and his associates imprinted a message, an interactive vision, in a pair of Sith amulets that later fell into the hands of Exar Kun and Ulic Qel-Droma. Ragnos and company had foreseen their partnership, and appeared to Kun and Ulic. Ragnos' message -- maybe even his spirit, since Nadd could jaunt about the galaxy as a shade, but Rave and I think it was literally just the message in the amulet -- appeared to Kun and Ulic. Ragnos touched their foreheads and branded them with their own Sith symbols, in the vein of the personal sigils that Sith Lords used in Ragnos' day. Oh, and if all this wasn't bad enough, the combination of those two amulets, when held by allied Sith Lords, was much more powerful than either one of them. Considering just one of them, post-Massassi-ritual, shredded a frigate-sized wyrm and one-shotted a powerful Sith Witch (Aleema Keto), it might be a good idea to find these amulets and keep them separate.
One final point, and it's far less dark than the above. A quote attributed to Nomi Sunrider, who had just discovered that Ulic had turned to the Dark Side. "Ulic will come by his own choice or not at all. That is the Jedi way." She was echoing her own Masters, who'd made a similar statement. And then she and the Jedi just...left. No attempt to 'bring him to justice' for being angry and having nasty friends. Just respect for agency and hope for change and faith in the possibility of redemption. Nothing high-handed. I like that.