Do federal court rulings (non-appeal) function as estoppel or persuasive authority for them to be cited as authorities in state court civil complaints when the question at stake relates to state laws?
That depends what the issue is. On constitutional issues, and on issues of federal law (which do come up in state cases) , they are binding precedent, at least in that circuit for an appeals court opinion, and in the whole US for a Supreme court opinion. District court opinions are not generally binding unless upheld on appeal. On matters of state law, the state's own highest court is the final word, but a federal opinion could be at least as persuasive as one from a different state.
to the best of my understanding one does not use the term "estoppel" to describe the effect of a previous judgement by a different court. If it is in the same case and not on appeal, the term is Res judicata ("A thing (already) judged"). If it is a general matter of adhering to clear precedent, the term Stare decisis (“to stand by things decided.” ) would be used.