It really does sound ambitious and im all in for it. As far as I understand these are good news no? Ringman content gets updated and improved with the story and timelines u had in mind making it A bigger and richer game. Being able to play as masuo through your 4 years history will be a charm, and I cant support you enough.
If there are so many quests, plots, outcomes, timelines (which im excited as hell, even without you helping us), the quest reset will be more specific (like resetting only a part of a quest or reset from a branching point, something like a scroll from lady mystery with a road that branches and we can return to either point, or will there be a different saves option?
And about the year system, will it advance when you reach certain points of the history no? The whole night and day cycle is not a time limit like after 300 days year will change.
Also, the lore and background for character profiles will change? or they will mantain their relations and backstories, all of the timelines you explained, etc.
Best of luck.