I have about 4 weeks of Blender knowledge.
Why is the line shown in the Bottom red circle not affected by the Subdiv modifier? It feels like it should be, but it leaves a sharp edge? I can't make sense of it.
Secondly. I want to keep the triangle shape shown in blue (top image), but from what I understand I have to turn all my faces into quads. My first solution is shown in the bottom image, but if I take that route I lose the triangular corner and introduce all sorts of wackiness when it comes to edge loops. Is there a simple solution?
The other highlighted problems are minor: There's a weird hitch in the edge shown in the top red circle which I can't solve without breaking something else. I'd also like to move the edge shown by the dotted black line to the yellow line, but, again, as soon as I attempt it, the models turns into a horror show.
.Blend files on Gdrive [1.6mb] (Pre and post edge looped) with references images if anyone's feeling extra charitable.