Pics -
As far as autos in a 5 gallon - that would be enough to sustain a plant for weeks. Depending in strains ( some are voracious eaters ) that amount of base medium should allow an autoflower grow up to a 100 day average in life.
At worst … an occasional topdress of fresh watered in soil ir dry bloom fertilizer to carry the last stages if flower. I find a lot of autoflowers not utilizing “ all “ of a 5 gallon size of soil sometimes. Some will explode in rootmass some not so much.
Autoflowers are like houseplants - they pull what they need from the base soil and only when they want. NOT by the grower dumping a bunch of unnecessary nutes into this already nute dense soil.