When you get to an individual level, I'd call it simple a belief, or a practice, or a cult (in the anthropological sense).
Those words may well also apply. Cults, for example, can be religious or secular. Religious cults are defined by a cult with a specific supernatural belief.
Religion requires an aspect of community.
Nope. You can have a religion of one person. You can have a religion of _zero_ people - there are plenty of ancient religions that have not stopped being religions merely because people stopped believing, or switched to more contemporary religions.
Without that aspect, it's just one person's opinions and customs.
Yep. And if there is a supernatural aspect to those opinions and customs, then it's a religious opinion/custom.
For example -
"I always take my shoes off when I go inside" - custom
"I always take my shoes off when I go inside because I fear God's wrath" - religious custom
I disagree. Civil religion illustrates that you don't need the supernatural to be a religion.
If a civil religion does not contain aspects of the supernatural or superhuman, then it is not a civil religion - it is merely a civil association.
For example, your local chamber of commerce is not a religion. If it started requiring all business owners to pray to Vishnu, then it would become a religious organization. If it started requiring all businesses to paint their storefronts a certain way, that would not make it a religious organization.
And there are other examples of religion that don't believe in deity or the supernatural.
Name one.