SUre I can help you,
yes the cramped 16 should be imported as a 16x16 tilesize tileset the tileset_8 can be imported with 8x8 and is a lot more flexible, but a bit harder to get a hang of. It will work for a lot of cases as it is, but for some games or ideas you have you'll need to manually adjust the guy graphics by a few pixels.
I personally recommend to build a backgroud image with the tiles, export the background image to use in the engine.
The slots could be added with the tileset, however given the spacing nature ui has in games, maybe you want to just put them in a layer above or a different aligned gridsize, to make them space nicely, as aligning them on a tilegrid most likely will feel bad in the game.
Buttons and other things you need to add manually in the engine on top, or you need to make a flattened background image.
Hope this helps you and clears up many points.