I think Michael’s parents should be ultra-straight laced, 50s upper middle class types. No skullfucking. They shouldn’t feature prominently - it should mostly be the Mike and Loomis show.
Hugh Grant as a possible Loomis.

He doesn’t look like Donald Pleasance, but he’s probably the best actor who might actually do it.
Maxim Swinton as Young Michael.
https://www.imdb.com/video/vi3050225689/?playlistId=nm8562769&ref_=nm_ov_vi

Atticus Mitchell as Young Adult Michael
https://www.imdb.com/name/nm3620184/bio?ref_=nm_ov_bio_sm


Looks close enough - I’m more concerned about matching Tony Moran’s look than I am Will Sandin.
I’d take cues from asylum movies like The Exorcist III and Session 9. Michael shouldn’t kill anyone on screen, but there should be a few mysterious deaths at Smiths Grove, both of patients and staff, that attract outside attention.
It would have to be a short series, maybe seven or eight episodes with one season. Not enough material to maintain interest in it otherwise. Play it very straight, and very dark - not necessarily overt supernatural elements, but definitely psychological horror elements. I wouldn’t overtly reference Laurie as Michael’s sister; you want it to be able to function as a prequel to all or the (non-Zombie) timelines. Have the Myers family bring a baby with them into the asylum at the beginning, but don’t mention her after, and don’t list her in the credits. If you want her to be Laurie, then the series functions as a prequel to the Thorn or H20 timelines; if not, then it works as a prequel to the 2018 timeline, or just to the first movie. Maybe slight teases at possible future developments - say, when we meet Dr. Wynn, he’s a fairly sinister character wearing a black stetson hat - but nothing overt, tying it into any one continuity. The point is that the series should be vague enough to serve as a jumping off point to any of these

You might even cast Tyler Mane and James Jude Courtney as asylum guards, just for fun. Have Dick Warlock, George Wilbur, Don Shanks, Chris Durand and Brad Loree cameo as inmates, if they can do it.