Could LMB be made to box-select when used outside of a model, but circle-select when initiated over the mesh?

Question

I'm trying to customise my Blender further, but finding it hard to set it up the way I want. A few of the things I want to accomplish in order of complexity:

Box select on LMB
Box select with consistent modifier-key use: Shift LMB to add to selection, Ctrl LMB to remove from selection.
The above, but additionally: releasing the LMB exits box select (confirms)
The above, but additionally: clicking over empty viewport starts box select, clicking over a mesh starts paint-select.

I know I can set Box Select to LMB click, but have found it kind of annoying without at least some of the other things I bring up. Are these possible, and if so: without much scripting?

Answer 1

'Box select on LMB'

Try setting this in User Input: 3D View --> Border Select --> Tweak, Left, Any

(Let me know if you made progress on the SHIFT-drag to add to selection, I am looking for that as well.)

EDIT: I discovered a partial answer. Add a new shortcut, use the same one (type in view3d.select_border) This time check "Extend" and "Shift." Now Box selecting with shift will add to the selection in object and edit modes.

However there still isn't a way to subtract from the selection that I've found yet. And I don't know how to unmap CTRL-select for adding to selection. Keep me posted if you find a way.