It is pretty common with a sex sling to use a stand. Many people are just not willing to put four hooks in their ceiling. If that is the case for you, I would recommend you take a look at our Stands page. Of course, if you are OK with four mounting points or you have a dedicated room for these types of things, a direct ceiling mount is a great option.
For a swing, most things are a general guideline, and there is no fixed answer. Your mounting options are limited in one direction by the spacing of your ceiling studs. In the other direction, I would aim to be near the higher end of the recommend ranges because it will be more comfortable for you.