You should ask only one question per question.
This helps everyone involved.
- You are more likely to receive an answer if you ask one thing, because you don't discourage people who know the answer to only one of several questions you have from answering.
- Those answering your question don't get tangled up in the details of several tangentially related requests and can focus on one specific issue.
- People with a similar problem will have a better chance to find the answer that helps them quickly and efficiently if they don't have to dissect an answer that addresses several points at once.
The point of a Q&A site is that you ask one clearly defined, abstract question that is useful for a wider audience.
I know it is tempting to stuff several requests into one question, because they seem related and it is easier to have to click the 'Ask Question' button and paste a code example once. And eventually someone who can answer all of your question might come along to answer all of your questions at once, and you will only have to copy and paste the code and you'll be good to go. Even though it might seem easer for you, for others this will mean more work, and it might even prevent you from getting good help quickly.
I don't think you can ask too many separate questions (even though some automatic quality contol system might disagree with me here) as long as they are good questions. Interesting, clear and overall good questions benefit everyone on this site. Take some time to describe the problem you have as precisely as possible, do some research, add an MWE, and try to make your question useful to others, give it a good title, ....
You also raise the point about editing questions after they have been answered. There was a similar question a while ago: When is it Kosher to edit one’s own question?
I agree with the sentiment of both answers and would like to draw attention to egreg's distinction between answered and unanswered questions.
It is fine to edit unanswered questions with additional information. I would even go so far as to say that you could change the question (other people may feel differently), in that case make sure that title and tagging is still appropriate. If no one has yet invested their time to answer your question, then no harm is done (of course you can't really know if people have played around with your question a bit, then realised they couldn't help you, and consequently didn't post an answer).
If you have already received an answer, you should be very careful to edit your question. If you edit at all, you should make sure that your edit does not invalidate the answers you got. You should not change the essence of the question, you should not add additional requirements and desiderata (unless clarification is specifically requested). Even seemingly minor details can require drastic changes to answers; that does not mean that minor edits are absolutely verboten, but it might be nice touch to comment on the answers first and be prepared to be asked to ask a follow-up question. You should definitely not edit your question if you only realised after asking or after seeing the answers that you actually wanted something different (XY-problem-like).
In the specific case you ask about you should definitely ask a new question. The first question was about
\ChoiceMenu. The second question is about the layout of
\ChoiceMenu. So while both things have to do with
\ChoiceMenu they are so fundamentally different that a new question is warranted here.
articlemay not work with
memoir). so before narrowing your question to a single small point, please think about this.