Re: How should I configure my home studio?
Yikes, that's a weird one. Also, that's definitely NOT to scale, which makes it tough to eyeball.
Gut level? I'd be more concerned about the hallway marked "basement continues" than I would be about the length/width of the room, since positioned based on room dimensions (facing the 13' wall, towards the window, centered) your left speaker, pointing inwards towards the right, would likely have a way more distant reflection point (somewhere down the hallway) while your right would hit the shorter wall. You also have the extra foot drop on the ceiling to contend with. There's no real ideal answer here, but I'd probably start by trying the desk facing the 18' wall with the hallway to your left, to at least get consistent airspace behind you, and then for kicks also try the opposite side of the room with the hallway behind you and to your right, to take the foot drop in the ceiling mostly out of the equation. I suspect the first approach will work better than the second, but acoustics are weird.
That said, if you don't mind getting your hands a little dirty, installing drywall and a door across that hallway to close off the room might be a better long term answer.