1. I noticed on another keyboard I use that if you long press on the space bar you have what amounts to an alt key to insert a tab space.
2. I would like to suggest that hitting the delete key, then swiping away from it deletes the last word. Hitting it normally without swiping would delete a space as normal.
3. Could you set up a feature that will bring up variations of a word if it is highlighted, or if the cursor touches the word. I don't know if SmartKeyboard can currently do this or not. If so, it's not obvious from the settings menu.