Hey! thank you so much, that really means a lot, and I’m glad it’s turned out more capable than you expected!
Your own items: Not fully yet. For an item’s inventory picture, you currently choose from the built-in library of item models (around 140 of them: keys, letters, tools, toys, lights and so on). You can import your own 3D models as .vox (MagicaVoxel) or .glb files using the Import button, but right now those can only be placed in your scenes as objects. They can’t be used as inventory pictures yet. Letting you use your own model or picture for an item is a great idea, and it’s going on the list for the next update.
Your own music and sound effects: Not yet, either. At the moment you pick from the built-in music and sound effects, which are all original, so they’re safe to use in your game and in streams. Importing your own audio files is also going on the list.
Text boxes: You’re right, some of them are too small for real writing. Thanks for pointing it out; I’ll make them bigger.
Development is definitely continuing: I’m using Mixel Maker myself to build a full horror adventure, and a lot of new features are coming out of that work. Thanks again for the kind words and the recommendation!