Inkscape is a fine program, but provides no automation for the schematic process. I would actually use Powerpoint or the free version OpenOffice Presentation. Powerpoint includes features like automatic connectors that keep lines intact as you move boxes around. Not very good, but better than nothing.
For the OP, if you are doing this only for yourself the electronic schematic programs referenced above do provide automation. You don't have to be constrained to typical automotive format. You will find yourself creating symbols for all of the unique components you are using.
Since you mention wanting to get something done this week, I actually would recommend Powerpoint or its like. You already know how to use it. The learning curve for any of the automation tools will set you back at least a week. If you already are conversant in AutoCAD that might also be a good option.