Those are my exact same dimensions. You won't be disappointed, but keep in the back of your mind if you have a baby now it'll outgrow it in a year and a half, maybe two if you feed it well.
If you're going for fancy decorations, I suggest getting a nice hide but putting it along the width of the tank; the 12 inches seems nice from the front but it doesn't really leave a whole lot of room to put things facing out of the tank, this is double for when the snake needs a bigger hide for when they get longer. Other then that, if you get a screen lid, get some foil along maybe 1/2-3/4 of the top to help with some humidity unless you use something in the coconut fiber family of substrates, since those keep moisture well and will help keep with humidity with regular sprays.