Thanks for the feedback! It's always interesting to hear what people feel is missing when they are exploring Spine.
1) If you drag an image file from the Images node into the viewport, Spine creates a slot for the image on the selected bone (or root if nothing is selected). We could create a bone as you suggest, but where? At the center of the image? After you place the image and bone this way, it is unlikely the bone would be where you need it, then you'd need to enable bone compensation and adjust the bone position or hold alt with the Create tool to redraw the bone. I'm not sure this is better.
Note the most common workflow is to use the Photoshop script and Import Data so all your images are in place, then you just need to create the bones. Since the images are already placed, they help when choosing the bone locations.
2) It's true, we added the rule but don't yet have guides. We will in the future!
3) Generally you want to use as few keys as possible. We could add a hotkey for this though.
4) The Scale tool is proportional by default, meaning when you click and drag in any blank space in the viewport. You have to grab the X or Y axis handles to scale only on one axis. Spine tries to avoid making you click or drag tiny handles, instead you click to select, then you can manipulate by dragging anywhere in the viewport.
