Joseph: The Shulchan Aruch quotes lots of Dinim. Some are D’Oraisa. Some are D’Rabannan. Some are Minhagim. And some are just Minhagei Chassidus. For example, it is quoted B’sheim R’ Moshe that most of the things in the first 4 SImanim of OC are Minhagei Chassidus. Washing one’s hands immediately after scratching one’s head or touching one’s upper arm, for example. It’s a generally accepted Klal in Achronim that when the Mechaber starts a phrase with “Lo” (instead of “Assur”) it’s just a Lechatchilah or Minhag Chassidus.
And I thought I explained this in another thread. The Rambam is referring to just Stam being outside. That should be only once a month. He explicitly excludes from that going to Simchos and similar activities (I don’t recall of visiting friends was also excluded but I think so; I’ll have to look it up again).