Hello! I'm not familiar with this game, but considering the mechanics mentioned, I suggest working on less complex games first, keeping in mind that you're still learning.
Since there are many (and somewhat complex) mechanics, you can learn one thing at a time (a draft game, with one or two mechanics implemented). Once you have this knowledge, you probably won't have any more doubts about organization.
Game jams are great for this!
But to answer briefly:
What's the best way to manage NPC relationships and personalities?
You can organize all the game progress in a JSON file, or use dictionaries and arrays to store these values.
How would you organize dialogue events between multiple characters?
I use a JSON file with all the dialogues and event triggers (which should be programmed in the event sheet). You can also use dictionaries and arrays; it will be simpler to learn, but more difficult to organize.
It's not something that can be explained in a paragraph... There's a lot to learn before that.
Is it better to use a global event sheet or separate event sheets for different game systems?
There's no difference; you can do whatever you find most comfortable. In large games, it's common to work with several separate event sheets for different mechanics and include them in a main event sheet.
Organizing them into groups within an eventsheet also helps.
Are there any plugins or tutorials for building daily schedules and random events?
I don't know, I don't usually use custom plugins. But it's a mix of the first and last questions.
What are the best practices for saving player progress in a simulation game?
Simply save the JSON with the player's progress to a file using the File System or LocalStorage.
Note that there are several ways to do each thing, including everything could be done with global variables and the save/load of the Browser object. It's a simpler solution to understand, but less performant.
Use the engine documentation as your guide: construct.net/en/make-games/manuals/construct-3
And learn the mechanics separately through the Construct tutorials: construct.net/en/tutorials
Good luck on your journey!