Suppose one question posting contains several question. If I can answer one question, but cannot answer all of the questions, is it ok to post my answer as an answer, and not just as a comment?
Yes, partial answers, given as actual answers, are acceptable and even desirable.
If OP of a question in some case should feel they prefer the remaining question as an unanswered question, they could in turn ask a new question, focusing on what is still open and what they have learned from the partial answer.
Of course, both should be done using common sense. For example, the partial answer should be still substantive, and a reasking of the remaining question should be done only (if at all) with some significant delay and clear indication of the earlier question.