Hello mate, I'm on the run so just a short answer, but you can always join our discord and discuss this further.
1. We can for sure add all weapons to the offhand, but keep in mind that this won't change the animations. The shooting for example will still just be visible on the mainhand.
2. Using our drag and drop spritesheet creator you can adjust the templates and the export names and add whatever you want to it.
3. In the new version busts can be between 500 and I think 144px big and you can choose to export busts or faces to be used with RPG Maker directly. The RPG Maker Mode toggle only changes between 7 and 3 frame animations and has nothing to do with the export anymore. 😊