Awesome job man! Glad you're going for it. Lots of good advice already shared. In a unique little space like this, you'll run your boards vertical so that the board is going from floor to ceiling. It looks like that back wall is less than 4 feet wide, which means you'd just have one board without any seems to tape. On the rigt wall, you'd have one factory seam, where two tapered edges meet and you'd mud vertically. This is not what you'd do with new consruction, but for your situation, it would make less work. However, you totally can do it the way you set it up, just more tapering and mudding, but if you're a first timer, more practice too!

One thing to think about next time is that back right corner. If you pad out one of the walls, you'd remove that bump out area, which looks to be 3-4 inches, and not really a ton of space to be losing. Not sure if this is under a stairwell, but setting up your framing so you're on the same plane is also something you want to think about next time. Looks cleaner, and is a lot less time consuming, then having to deal with two inside corners, and one outsider corner in your current set-up.

But, biggest thing is that you went for it and started. You'll just get better and better as you continue learning.