It is a tricky subject to try and harmonize some of God's commands, though they are never contradicting in any way, simply because of our weaknesses as humans. Our understanding of the law and the law itself are obviously two different things. I would deny that the creation mandate overrides anything in the moral law - they are completely in harmony. Obeying the moral law in our families, churches, and civil magistrates is in fact the only way to fulfill the dominion mandate. But so far I've not seen anyone try and justify birth control based upon the idea that it would cause the couple to disobey the moral law. If this were the case, then there would obviously be some cases in which birth control is not only justified, but sinful to neglect! Those types of situations are much more difficult to assess (like if the life of the mother was said to be in danger) but struggling with finances in no way violates the law of God unless that struggling is caused by selfishness or some other sin on the part of the parents (probably mostly the father). In this way, I think it is actually quite difficult to take a stance of "liberty" regarding this topic. If things like financial struggles justify birth control because it causes the parents to disobey the moral law, then there's no such thing as liberty not to use it; they would be required to use it in order to uphold the moral law. So saying that our use of birth control needs to be based upon the moral law actually throws out many, many (if not all) arguments in favor of birth control. I certainly do not have it figured all out, don't get me wrong - the fall definitely complicated matters, lol. But generally speaking, all Christians should be opposed to birth control because the principles behind birth control clearly contradict the principles behind childbearing in Scripture. I hope that I understood your points correctly and it is indeed nice to meet you too!