If you are setting this up from new, you should be using chan_pjsip, not chan_sip! Some information for that can be found at https://wiki.asterisk.org/wiki/display/AST/Setting+up+PJSIP+Realtime, but I haven’t used realtime myself, so cannot be sure that the information is correct and complete.
Normally with chan_sip, you should only have SIP peers. Users are often used because of old cook book configurations and a mistaken belief that you must have separate entries for inbound and outbound. Whilst there are rare cases when friend or user are appropriate, in must cases they offer no advantage, and can result in unwanted behaviours.
Generally, if you are using real time, it is because you want to make frequent changes, so you should be more interested in the mechanisms for changing the data, that in those for initially loading it.