Since Kangarube already answered the first question:
2. I don't know how long it'll take to finish the game. Last year I made the estimate that it'd take me two years to write the rest of Minotaur Hotel, and I guess that estimate was true for the assumptions we had back then but since then I've had to put on many hats. Wattson is a great programmer but there are some tasks that only someone with a deep understanding of the characters and their introspection can do, like picking their expressions, and under our current structure that falls to me.
I'm hoping that once Chapter 21 is finished (written, edited, implemented) I'll be able to pin down a real estimate of how long it'll take to finish the game.
That said, after Minotaur Hotel is done I intend on writing more stories set in the same universe. I already have two games on the outlining stage. A few years ago Alpha0 told me that Minotaur Hotel was my Disco Elysium and I guess that's true, this is an universe I wouldn't mind working on for many, many years.
So, if you want me to keep going, buckle up. You're gonna get what you want. I don't plan on stopping anytime soon.
3. There's no "most canon" route, and "routes" don't really describe how MH works, but if I had to pick what set of actions lead to the playthrough I find the richest it'd be:
1. Figure out all of Argos' puzzles and translate the pages of the Argoi's diary. figure out who he is before Chapter 18.
2. Take every opportunity to associate Jean with Hermes -- make the toast to Hermes in front of him, and name yourself as "Hermes" on his phone.
3. In the Hinterlands, complete the skinless god quest and take Pedro to the pond, then follow the trail to the shed.
4. Optional: In other playthroughs explore the expanded hinterlands for more magical realism shenanigans, and visit the Small Cabin in Chapter 20.
5. Optional, but highly recommended: Prioritize hanging out with the staff over Asterion's translation project. Go for as many hangouts as possible with your favorite characters.
The first 3 points activate what we internally call "Detective Mode", which triggers some unique moments and lines. I consider that to be the most literary playthrough style, it provides more insight on some key aspects of things.