It took a while, but there have been some pretty big improvements.

• Transition to 1440x960px: I eventually found that being limited to 360x240 was going to be very limiting, specially with text because at low resolutions it looked like a jumbled mess. Thus I embarked on a pretty hard journey (not hard in retrospect) to figure out how to change the resolution but also keep the pixelated style without having to draw sprites at 4 times the resolution. The solution I ended up finding was to store a scale factor of 4 (360x4=1440, 240x4=960), and then scaling a separate surface to that resolution. Now, a surface is created with the same dimensions as the map, and everything is drawn to that surface instead of the map (I used to draw enemies, turrets, bullets, etc. onto the map because they moved together), and then that surface gets scaled. This allows me to keep the pixelated graphics on the actual game, and have crisp text on the GUI. For the offsets, I just moved the function that translated the screen coordinates to map ones from the map to the scene, and then adjusted it to take in the scale factor. Everything else works pretty much the same, as its only the image and mouse clicks getting scaled instead of rectangles. I scaled the button sprites to 32x32 to make them easier to draw, and then I have it in the config to scale them to 64x64. I decided to do that mostly for ease, because most of the other sprites are around that resolution anyway.
• Turret placement: I added more buttons to the GUI and added turret placement. The GUI itself is always going to be kind of janky. I moved it into its own class so as to sort of clean up the code in the main scene, but now the GUI manager does weird things like self.scene.game.screen.width which isn’t very pretty. It’ll do, though. I track a variable storing the turret to be placed (None if it’s not in that state) and a variable that stores whether it can be placed. I check for collisions between the path tiles (I knew it would be useful!) and the sprite to check if it can be placed. I also modified the draw function of the turret to make it red or green depending on it.
  GUI: Generally, for the GUI, I keep a state from an Enum (basically a fancy way of storing a string for a state), and then change the UI according to that state. I designed it in a way where it only rebuilds it on command, so it won’t rebuild the whole thing every frame, in hopes to save some sort of performance.

Overall, some very good progress, even if it’s not 100% visible!