The linked questions are examples of FAQ-style questions: the question post poses a number of (possibly related) questions, and then each answer seeks to address one of those questions. Generally speaking, such questions are not on-topic on Math SE. We expect questions here to be narrowly focused, and centered on a single problem or mathematical confusion.
FAQ-style questions are, as rschwieb suggests, less searchable. They are also more prone to disorganization, as users other than the original asker/answerer may have alternative answers which are likely to get lost in the shuffle. It would be better to pose each question independently (though it might be reasonable to interlink those questions).
It also seems that the question of self-answering is implicit in the question, i.e. is it acceptable to self-answer a question?
In general, asking-and-answering a question is perfectly fine. Indeed, the software and design philosophy of SE encourages users to answer their own questions. However, there are some things to keep in mind:
One of the primary goals of Math SE (and the SE network in general) is to build a repository of questions and answers which are of interest and use to a large number of people. The goal here is not to create a solution guide to a particular text book, nor to show off esoteric knowledge. When you ask-and-answer a question, you need to make sure that both the question and answer meet the site quality standards (indeed, we might even ask for a little more, since there is an implicit claim that the question is going to be helpful to a large number of users—it certainly isn't going to be terribly helpful to the asker, since the asker already knows the answer).
The site standards are summarized in the meta topic How to ask a good question. Note, also, that any Q&A in this style should contribute something new to the site, and should not (except under very rare circumstances) duplicate an existing question.
A similar, though distinct, situation in which self-answering may be desirable is in the context of a question rewrite. In this case, it is perhaps expected (though by no means required) that you will want to answer the question yourself. Again, just make sure that the work you do complies with site guidelines.
It is also not unreasonable for an asker to pose a question, then have answers (or hints) given in the comments. In such a case, it is entirely appropriate for the original asker to take what they have learned in the comments and write an answer. Again, please ensure that the question and answer meet site quality standards.