I have not asked that many questions, so I do not really know. Basically I just revamped one of my answers where I corrected the sheer ignorance in it and actually found the answer to the question (or at least I believe I got very close), but I do not know if the user who asked the question already sees an alert that I edited it or do I need to notify him with a comment?
No, edits to answers you have written does not give the person who originally wrote the question a notification that your answer has been edited. The OP will just have to check and see if an answer was edited by reloading the page. If you are still not sure that they are going to check, then you can use @username to tell the person that you edited your post to improve it.
However, please note that if the user does not respond when you use @ it is common courtesy not to continue to use @username because the person may be offline. This is because when they get back online their notifications will be filled with messages from you that you edited your post, and this can become annoying.
No. Notifications of edits go only to the author of the edited item (assuming they are not the one who edited) and not to others. (See this 3+ years ago request to make it different: Notify question OP (and those who marked it a favourite) if an answer has been modified)
You can indeed add a comment to the question if you like - you should delete it the next day (or sooner if the person responds in a way that lets you know they've seen it.)