Haha I must confess I had similar thoughts already! I really like our little reading group here, and the pace of ~2 books a year kept me on it without it being tiring. So if y’all are interested to continue with a different series, I’m in!
For the we could read, it seems that you did quite some research already!
I also have one series I want to throw into the ring:
Uchida Yasuo is one of Japan’s most prolific writers, and he created the Asami Mitsuhiko series that contains ~25 volumes: 内田康夫 - Wikipedia (but from what I saw so far, the volumes seem to be around the 300 page mark which makes them much more digestible than S&M imho).
I started the first volume already a year or so ago but didn’t get far because of life, work, and other book clubs, it seems. 
It seems more or less each volume is set in a different prefecture, which is also interesting as we can learn something about Japan on top of solving a mystery. The series seems to be extremely popular in Japan with lots of media adaptions. It seems to be a classical hobby detective series.
Ah I think they read at least one of the series’ books over at Natively: Home thread for 十角館の殺人! 🕵️♀️ 推理小説読書会 | Mystery Novel Book Club 👮♂️ - Book Clubs - Natively Forums
Uh. We also read the first volume in the Natively mystery club: 👁 Home thread for 眼球堂の殺人 ~The Book~ 👁 - Book Clubs - Natively Forums but yeah, “similar in vibe” says it all, it was so exhausting and boring that I dropped it about a third in or so…
Ah, this one right? 戯言シリーズ | L35
Is it that one? Amazon.co.jp: 虚構推理 (講談社文庫 し 110-1) : 城平 京: Japanese Books - that was a bit hard to find. Sadly Amazon doesn’t seem to have a series page for it. I think that’s interesting because the author seems to be quite young.
Oh, the pseudonym fooled me into thinking that the author is a woman 
This seems to be the first volume: Amazon.co.jp: 新装版 ４６番目の密室 (講談社文庫) eBook : 有栖川有栖: Kindle Store - sadly again no series page in Amazon but here is the list of books in the series: Alice Arisugawa - Wikipedia
Which would be this one: Reito Nikaidou | Japanese Mystery Wiki | Fandom with the first book here: Amazon.co.jp: 地獄の奇術師 (講談社文庫 に 22-1) : 二階堂 黎人: Japanese Books - big boi at 550 pages
I think my preferences would be:
- no buildings/architecture (which would speak against the 館 series and the Hall series)
- preferably no locked room murders (I dunno, these are so omnipresent in Japan, probably because suicide is such a common thing, but I had never heard of this genre before I started learning Japanese
- I don’t think I ever came across one of those in German murder case literature, and it doesn’t really click with me, probably because it’s more about some clever room-locking trick rather than some clever murder trick 
) - ideally average-sized books (i.e. around 300 pages, up to 400 is also fine on occasion)
I could also imagine that we narrow our preferences down to three or so series, read the first volume each, and then pick one that we read further?