What are issues to consider when making your code for an experimental paradigm, which was conceived by someone else, publicly available?
Are there legal issues, such as copyright infringement, to be considered for commercially or non-commercially available software? Note, I created all of the code and all images based on low resolution prints in publications. I'm merely copying the concept.


Unless their method is patented, no. Software is covered by copyright which protects a given implementation, not the general idea. Just as you are allowed to write an own novel on a topic that is covered by existing novels already. 


  Would such a release conflict with common etiquette in the case where the software is simply not available from the original authors (remember, I asked but got no reply)?


No.


  Is it necessary to ask each author before releasing my code?


You need to get permission from all copyright holders. Depending on the actual settings, that means: for each author who contributed to "your" code the acutal holder of the copyright (could be the author or the author's employer). 

The authors of the "original" software are not involved at all. 


  Can I be held responsible morally if the software is used and turns out to be faulty? I'm less concerned about legal responsibility because the license I intend to use does not provide warranty. More importantly, I certainly intend for the software to work since I'll use it my self but you never know.



moral responsibility: just like you will be held responsible for any other scientific publication. 
legal responsibility: while no liability clauses are common for FOSS licenses, completely excluding liability is not possible in all legislations (e.g. in Germany a general no liability at all clause is/can be invalid).  



  If my study ends up being published and points to the availability of the software, can this benefit the citation count of the publication?


Definitively, yes