Like you mentioned, introducing the source in the first line is usually what is done in case of citing the same source multiple times in the same paragraph.
You could state the first line as something similar to
The product documentation (inline citation) states that blah blah blah
Now you can continue writing the rest of the lines in your paragraph. Keep referring back to the user manual. For example,
The manual mentions
Based on the recommendations in the manual it is apparent that
blah blah, as defined in the user manual
and so on.
When changing the paragraph you can continue writing in a style that keeps hinting that you are talking about the same source. As long as you have not introduced any other references in between, you should be good to go.
Depending on the information that you have from the user manual, your inline citation would change. For example, if by any chance you have the name(s) of the authors, you will be using that in the citation. Else, as mentioned in the answer herehere you can simply refer to the user manual with a n.d. mention. Or you may choose to attribute the authorship to the Organization (depending on how the user manual is written).
To address the last part of your question, if the information that you have is too general and obvious (like common sense), you may not need to cite it to any source. However, if the information is borrowed from a source (which I think is your case), you will have to mention the source. Do it once in the beginning and then keep writing. In the references, mention the complete reference. Have a look at the second last answer here (citing Apple's user manual).
Hope this helps!