For better or worst this series is similar to SAO in the fact that the villain for the second arc is the most hated in the series. Some hate him as a character while others hate him in the same way that you would any villain, but either way he is very formidable.
This second arc will have the most connections to SAO, and I doubt you will miss any of them (By the time you read this you might have already run into one). Also, keep in mind that even after everything that happens in the anime (and the novels), people still try to deny that they are connected, pointing to something that Reki said years ago right around the beginning of the Alicization arc for the novels. He had said that for now there was no connections to SAO so there was no way to say if they were connected or not. At the time that was mostly right since we knew nothing about what Alicization would entail. At the time the novels were only up to the part that Kirito and Eugeo started their journey, or the end of episode 4. Even pointing out some other things later in the novels people still stay adamant that they are not connected.
Also, the English release of Vol 22 for SAO releases on the 22nd of June and although I’m not as excited for this one since it’s not the continuation of Unital Ring, it still has some short stories I’ve been wanting to read for a while. Most importantly it has Sisters Prayer which revolves around Yuuki and her sister. Hopefully they turn that short story into an OVA or something like that in the future. Especially since they have time while Reki finishes Unital Ring.
As an update to some movie stuff, it’s basically confirmed that he new character that will be anime original for progressive is being written by Reki himself (Unlike some of the changes made to the Alicization anime). Apparently, most of those scenes will happen before the beginning of the first volume and serve to explain how Asuna ended up where she did at the beginning of that. Reki says it works with the story even if it wasn’t intended to be there originally, so I trust it will. My only issue is that I’m sure he will try to retcon it into the novels and I don’t know how well that will work out. Yet again the Augma was retconned into the novels and that worked out pretty well,so we’ll just have to see what happens.