I am happy you had a good time with AGOT, and feel free to post the guide! I have no real idea how many people are making it to the ending, but the ending is what I am happiest with, so if the guide helps more people get there than all the better ^^
I thiiink the only quest you are "forced" to do is escaping the oubliette, which forces you into being level 5. The only encounter that is stopping you from fighting Phlogiston at level 5 is the drone encounter, which can't be avoided and is between you and the switches needed to open the final hallway. I think the drone is balanced around level 12, I'd have to check the numbers, but you can probably beat it a little earlier with the right abilities and speed order? It's designed to quickly dump you in the trash if you're too low in order to point people elsewhere.
But past that, yeah, I don't think there's any other required encounters, just practically you need to be strong enough to beat the drone and Phlogiston. Given how some of the quartz is blocked by fixed encounters there is kind of a "soft requirement" of levels needed to get more levels, but I think you could possibly get from 5 to 13ish without additional fights if you're quick enough and the pathfinding works out in your favor.
I am happy you found a lot to enjoy in AGOT; I have always struggled to hold my creative stuff with positivity and the general reaction to AGOT has given me a lot to think about in evaluating my perspective. I'd be happy to have you try my other works as stuff comes out of the workshop, of course, and I'll keep an eye out for your things too! :3