The Steep and Hike workouts don’t reference carrying weight of any kind or if I should wear my mountaineering boots, at least early on.
Yes, weight is added later in the plan.
For the steep workouts, the best steep sections I can come by require an approach and also repeating the hills, which extends the total time out quite a bit. Is that reasonable relative to overall weekly volume?
If it’s not interfering with recovery or life, then it’s no problem to extend sessions below AeT.
Lastly, if my hike should be 2hrs and requires 2k feet of gain, but I can’t find a hike that does that vert in the time (unless it’s very high angle), is it reasonable to extend the hike time volume?
Again, yes, if it doesn’t cause issues elsewhere. You’ll need to work with what you have, so I would prioritize volume, getting as much gain as you can in that time, and increasing the volume when appropriate.