(In no particular order or preference)
Ctrl+drag right/left = increase/decrease size
Ctrl+drag up/down =increase/decrease hardness
Alt+drag right/left = increase/decrease flow
Alt+drag up/down = increase decrease transparency
Hold right mouse button+drag to duplicate (selected)object on the canvas/workspace.
Short key menu:
Add a tab where users can assign options to the context menu of any tool.
(with presets for customizing toolbars/shortkeys/contextmenu settings)
Add an export button to the toolbar or menu with drop down for common file formats and a link to the export persona.
Make the export options wider and the real estate of it fit the more options in one screen.See here
Make the document background a (initial) locked layer so one could use the real estate around it as a visible/usable pasteboard.
Objects outside the document layer on this paste board should be ignored on export.
Have (initial) locked guides layer above the document which you could hide/show in the layers panel.
Users can create lines and/or shapes and draw these to this layer or copy/paste to it to make diagonal or odd shaped guides to snap to.
This layer should be ignored on export but be saved in the Aff file format for reusability like grid/layout templates (on MasterPages in APu)