Huyang showed up in a Clone Wars storyline that depicted Padawans training and learning to build a lightsaber. I think that was his only appearance prior to this show, and just like this episode, he had a ton of lightsaber components so that each Padawan could build a blade that was unique to them.
As for the episode itself,
I agree, I was surprised how little was resolved, although I figured it was inevitable that Thrawn would return to the home galaxy since they've clearly been setting him up as the big bad since season 2 of the Mandalorian. I like that the fact that he knew Anakin/Vader affected how he approached Ahsoka, and that he's learned from past encounters with Jedi to take them very seriously. I should have guessed that some of the characters would end up stranded, because Baylan and Shin are still on the planet, though to be honest I had forgotten that until the final minutes of the episode. Someone will have to confront them. And hopefully Ezra has the location of the planet in the computer of that shuttle he stole so the New Republic can build one of those giant hyperspace rings and go rescue Ahsoka and Sabine.
I'm assuming that all those boxes taken from the fortress are more Nightsisters in suspended animation, since Ezra mentions how Thrawn "woke up" the great mothers, and his Star Destroyer was headed for Dathomir at the end of the episode. General Grevious pretty much committed genocide against the Nightsisters during the Clone Wars, so perhaps they're repopulating the planet.
And there was Anakin at the end, watching over his former apprentice. We've got a seven Jedi line of succession now: Yoda - Dooku - Qui-Gon - Obi-Wan - Anakin - Ahsoka - Sabine. I think they've done a good job of reminding us of who Anakin was before he became Darth Vader, something that was again depicted quite well in the Clone Wars animated series. Ahsoka remembers him fondly, even knowing what ultimately happened to him.
My only real disappointments: no Captain Rex in the present day (though he may be dead, given the accelerated aging of the clones), and no Zeb, the only Rebels regular character not to appear. And that's odd, because they gave Zeb a cameo appearance in the Mandalorian, so they've built a CGI model for him, only to use it for less than a two minutes.
Very good series, though the pacing felt more sedate than I'm used to with Star Wars, which is typically non-stop action mixed with a few quiet scenes. But I felt like the story unfolded in a manner that made sense, and characters went from point A to point B without me ever wondering just how they got there. I liked the first intergalactic travel in Star Wars on screen, though I expected a different galaxy to be more exotic in some way. The planet felt like it could have been any planet in our familiar galaxy. Overall though I really enjoyed the series, and I am hopeful that we'll get another season and tie up the open storylines.