Reddit does have members that post credible leaks. Many GOT leaks are spread by people on Reddit. Idk if this reddit poster is credible.
I'm inclined to put some stock in the sabre rumor because it fits with what happened in TLJ and what's been established about crystals. The broken crystal can be seen in the TLJ prop and in a close up in the film. Canon says that breaking or cracking has a serious effect on the crystals. Kylo's crystal is cracked. If JJ sticks to what was established by TFA, TLJ, and the new canon the Skywalker crystal should be unstable and act like Kylo's. Whether JJ sticks to what's been established tho...he could just choose to ignore the crystal being broken in favor of keeping the Skywalker sabre in it's original form.
The knights of Ren being all women sounds like something Disney would do, but it also sounds like the sort of rumor some basement dweller would make up to upset some of those idiots that dont like a bunch of women in star wars or to just piss off the Disney haters. Frankly I dont want it to be true, because I dont want to listen to people *****ing about the Knights of Ren being all women or anyone griping that a chunk of the female cast is playing evil characters. Not to mention it raises questions about the Knights' relationship with Kylo. Questions Episode 9 probably wont have time or Disney's approval to answer. Itd just be better to make the Knights a mixed group.
Kylo having his own special Troopers wouldnt be much different from Krennic having those Death Troopers in Rogue One. Plus those Kylo Troopers could be his version of the Praetorian Guard. So I think that's a real possibility. Tho if they are in the film I dont expect them to do much more than the typical Troopers.
Rey's outfit, well, we can safely assume she will get a new outfit. She's in a war. Armor seems appropriate. The Jedi during the Clone Wars wore some armor.
Kylo having the evil dark side eyes could go either way. Nothing ruling it out or guaranteeing it.