Hey, thanks a lot for the comment!
Regarding the add files/folder button, as well as the export path, these are using an external cross-platform library to browse files. I'll try and figure that one out asap and have it fixed for you.
Not being able to change the window size was, frankly, an oversight on my behalf. This'll be included in the next update.
Regarding the texture - Magicavoxel's texture is effectively just a palette, and it's extremely similar to just a material or vertex colour export. A good amount of MV's lack of optimizations come down to the texture file, as it means you're unable to reduce a multicoloured surface into it's optimal amount of polygons. In effect, MV's texture is what causes the models to be inefficient, so it couldn't be supported easily.
Hope this helps. If you need anything else or have any other comments then just let me know.