By definition, the only category of organism that meets those criteria are primary producers. This is because even a broth of carbohydrates used to culture an organism would need to be produced through photosynthesis, and so would therefore be requiring something made by another organism or ecosystem.

Rather than relying upon nutrients produced by other organisms, primary producers create their own. The most simple known primary producer are Cyanobacteria, and this phylum of microorganisms are thought to have played a key part in terraforming Earth and produce a huge amount of the oxygen we breathe.

Therefore, based on your parameters, I would say, Cyanobacteria are likely the most simple organisms that are self sufficient and contain minimal code. They would just need nitrogen, phosphorus, water, carbon dioxide and sunlight.

TLDR: all organisms except primary producers are in some way parasitic when you consider that they rely upon the outputs of other organisms within their ecosystem

Depends on your definition of an organism/virus, and what your function of interest is.

For example, if you're simply interested in things that can make more of themselves like viruses do: prions contain no genetic code at all and are simply misfolded proteins that cause other proteins of the same type to misfold into the same conformation.