Having lived through all of this I can never find any personal enthusiasm for Shim/ST mixing. I'll never discourage anyone from trying, have fun!, but consider it a gift if it works, and maybe don't assume if the math seems to work the parts always will. Shimano got it right but Suntour never did, and there's more real-world reasons for it not to work than to work.
If it's any consolation (I think it is), the rather difficult setup issues that you have correctly outlined in good detail are somewhat remedied by the availability of more-modern chains.
In particular, the overshift-sensitivity that you mentioned is lessened greatly by use of a modern 9sp chain on the 7s Accushift systems, to the extent that I can hardly find fault with my command-shifted setup ridden back-to-back with contemporary bikes.
I also don't recall Suntour having offered any sealed housing ferrules back then, which can do so much for the service interval of the cabling.
I thought that the 6-speed Accushift systems were relatively robust back then when the proper chain was used, but the 7-speed Accushift systems really begged for a narrower chain, mainly to deal with Suntour's narrowed spacing between the bigger cogs.
Having raced on their 7-speed indexing systems in the early-to-mid 1990's, I would tension the shifter screw as tightly as possible to better control the overshift, but I would have really liked to have one of the subsequent even-narrower chains instead of the IG and Sachs 8s chains that I preferred.
I made my own cassette spacers and used a Titanium cogset on a narrowed Nuke-Proof ti freehub to work with those 7s Command shifters. I bought everything cheap at the Encino Velodrome and other swap jumbles.
I even modded my Superbe Pro rear derailer to float as a full servo-panta, by discarding the b-tension screw and internally adjusting the cage spring tension to optimise the chain gap.
Somebody tell me it was worth it!