A rediculous dieity, some brainless believers, and a demand to donate one tenth of your saliry.
It seems to work.

I have a personal religion, recognized by me, congregation of one.

My spiritual views were developed and customized from my understanding of several sources, but mostly fall under the larger umbrella of "Spiritual Humanism" which is recognized by every state in America, as a religion and my being a clergy member of Spiritual Humanism (because I clicked a button that said "ordain me" ) allows me to legally marry folks.

"Spiritual Humanism" is a denomination of the larger umbrella of "Humanism" which also includes "Secular Humanism" which sadly is not recognized as a religion, however I believe many if not all states now recognize "Humanism" as a religion as far as licencing celebrants to perform marriages legally.

And so on... My belief is that the term "religion" means your method of feeling a connection to the source of your creation, whether you call that source God or Nature or what have you, and touches on your place in the world, your role or purpose, and the collective wisdom and philosophical truths you have gleaned from a mythos, or literary works, or traditional values passed on from relatives, new social truths you discover on your own, etc., Your religion should be ever changing, ever growing, ever adapting to your life and the world around you.

What constitutes a religion?

From your description, it seems you have reduced this question into misleading details. By reducing this question, you have duped yourself. Let me point your mind in the correct direction.

1. Disputable and shaky premises about the nature of the universe.

2. Mandatory norms that have no referential foundation, aside from a highly reduced view of positive versus negative norms.

3. Emotional thinking.

4. Conflation of religious texts, speech, and other things that are effectively language, with unrelated constructs like politics, everyday living, etc.

5. Belief in the existence and natural power of a deity(s).

6. Being so spooked to the point that one cannot function.

7. Wasting time with feel-good things like visiting a house of worship. Yeah, medicine ruled out such implications long ago, but some people want to praise-break for a few hours like a bunch of dysfunctional animals.

8. Baiting and switching. For example, we have week zero. On week zero, we discover that the scripture can be read like any other book. On week one, we discover that there are several professional and officiated interpretations to this scripture. Holy hell, did the deity in question actually want us to believe in this? It's not looking like it!

Now, how many followers, possessions, administrators, and rules make up a recognized religion?

I don't know, but that is searchable, probably.

The first rule of Fight Club is....

"Religion" and "recognized religion" could conceivably be two very different things. I use the word religion for whatever practice a person uses to maintain their peace of mind. I am the only person I know of who practices my religion (I invented it) but it serves me well, and apparently better than most "recognized" religions serve their followers.

That's an excellent question. The lazy answer is "a system of worshipping some deity or other" but there are atheistic religions (most Buddhist sects, Taoists, probably others). To me a religion is a system of dogma and rituals that claims, via esoteric knowledge into which you must be initiated, to have an accurate explanation of the meaning of life and the true nature of reality. It USUALLY involves one or more deities, but doesn't have to. It USUALLY has a clergy or priest class, but doesn't have to (e.g., Quakers and Plymouth Bretheren have no fixed leaders, members take turns leading / teaching the group). They USUALLY have a holy book or books, but not necessarily, and the degree to which they are revered or slavishly followed varies.

The common features are an accepted body of (almost always capital-T) Truth; traditions, practices and rituals to transmit and cultivate an understanding of the Truth; some form of demand for belief without a requirement of substantiation of any kind, almost always including alleged supernatural beings and/or realms and/or some form of afterlife; and a tendency to discourage independent inquiry or critical thinking.

As others have suggested, a "cult" is just a newer / smaller religion that is less established, and marginalized by the larger and more esablished religions and perhaps by the host society.

The degree and methodology of authoritarianism and ruthlessness and violence vary greatly as well, but all three of those factors are invariably present to some degree, however small.

One idiot to start them all.

When you think about it, the term "recognised" is irrelevant , you can belive any damn thing you want,

I don't know, it's not a football team.

One leader who either thinks they are a god or prays to a higher power.

That's it's big enough to not be considered a cult anymore.

Church of Body Modification is a thing. They achive enlightenment though tatoos and piercing. And they are tax exempt.