The Inquisitors seem to be a big sticking point for a lot of people who didn’t watch Rebels or play Fallen Order. I think the important thing to remember about them is that they’re not the top-tier villains or even proper Sith, they’re just the morally-bankrupt bottom-rung ex-Jedi who sold out to survive. They’re not quite cannon fodder like stormtroopers, but they’re very much expendable (in Fallen Order you fight a few as literal videogame bosses). Being a threat but a bit of a lame one is kind of their shtick - in Rebels at least they mostly exist as warm-up baddies to make Vader and Maul even more intimidating by comparison.
I imagine opinions about the villains of this show will improve now that Vader, the real threat, is coming into the picture. He ought to carry his usual presence, assuming the voice work and physical acting is up to scratch. While the Grand Inquisitor definitely isn’t really dead (because continuity), I think his wounding has been introduced to make him a severely reduced presence in the second and third acts. He is definitely the same guy because he appears with his Rebels look in comics set before this series. Reva will probably be separated from the rest of the Inquisitorius for the rest of the show, but keep interfering with Kenobi and Vader to continue serving the role of ‘character whose fate we don’t already know so there’s actually some dramatic tension’.
Re: how she knows Vader’s identity - we see at the start of Episode 1 that she was present at the Jedi Temple when Anakin Skywalker’s 501st Clone Legion started shooting everyone, and she may have even seen him killing Jedi himself (he only wore a hood, not a great disguise). Even if she only suspected it, Kenobi’s emotional response to hearing of “Lord Vader” would’ve confirmed it for her. I don’t think it’s so far-fetched to think quite a lot of the more clued-in Imperials who had been around since the days of the Republic would at least harbour suspicions - canonically Tarkin and Thrawn are basically 100% sure and Ahsoka figures it out based on vibes alone, so I’d imagine people like Wullf Yularen or the Inquisitors could also piece it together. I’m sure mentioning it to Vader’s face would be fatal, of course.
This show is definitely pitched more to the Prequels/Clone Wars/Rebels generation in its tone and characters, rather than being marketed towards OT fans like Force Awakens was. I think at this point Lucasfilm recognise that that’s the core audience these days, and even the breakout stuff like Mando seems to be designed to indoctrinate newbies into watching TCW and Rebels. With Filoni’s large role in TV even outside of projects he’s actually writing, that’s the current “Star Wars”, which is great if you like it, and not so great if you don’t.