Your over thinking this, If its just the inner kick panel then no bracing is needed , That panel ads no structural support to the door, You don't need bracing for the out either and I would leave the door on for the outer so you get a good gap.
If you do hinge pillars then yes brace it. Otherwise its just a big PIA to get around. try to remove the weather strip channel intact if possible and cut out whats bad in the panel. treat the inside of the cowl with rust inhibitor. Usually if the kick is rotted then the wheel house is as well. I've done many many cab reconstructions and don't brace for those panels
Something like this needs bracing
http://www.thehollisterroadcompany.com/media/Owencab/42215/owencab%20002.JPG
