I feed my auto's with veg food until about week 3/4 or when I see the plants start to pre-flower. Then I feed with bloom food until 10-14 days before harvest. Then it's just plain water till harvest
At best my autos are around for 11 weeks tops I very rarely feed at all, if all then its some (N) come weeks 3 or 4 ..I find the scecret to be the quality of the mix rather than the addtives
Like vostok mentioned....a good medium is all it takes for growing autos. You might want to add some perlite for airy-ness.
Rarely do we use nitrogen in growing and limited amount of phosphorus....autos do their own thing being a quick plant seed to harvest.....and they are quite nice watching them morph daily when budding starts.