Wait... Mazda made cars that werent powered by a triangle?
Id assume there are as many ways to turbo a mazda 3 as there are ways of turboing anything else. Unfortuantely i have nothing significant to offer to your checklist other than the following. Its possible that the turboing of automatic 3's isnt done very often because the drivetrain cant handle the additional torque or power produce by the turbo... Or maybe the ECU cant cope and tehre isnt an adequate piggy back and standalones our outrageous for most speed3 conversions? Good luck with the build tho, keep us triangle folks updated and maybe we will bump into something that may be useful for you along the way...