Show me your definition of GOD(s).

[Ryantology]

Quite simple really - if I talked about the "largest planet ever"

We wouldn't know all its attributes or be able to even imagine specifically what it looks like etc - but we can know that it's there. We can know it.

Likewise if there were such things that were beyond human perception but knowable through their effects around us (e.g. a human mind) we could get to know it but not understand it.

Not taking any presumptions there cannot be things that are beyond human perception, you can see that there are many things we can be aware of and not fully understand.

What if you talked about the "largest planet ever"? And why is this a terrible analogy?

First, we know planets exist. We live on one. We can point at it and say "planets definitely exist, here's one for you to look at". Right away, the comparison breaks down because there are no gods to point at. To say that any real physical object has a 'largest' counterpart is not a leap of faith, it is a physical certainty.

How about the 'largest'? Planets cannot be indefinitely large. A planet which acquires enough mass (around 15x Jupiter's) will become a brown dwarf star because there is enough pressure in the core to ignite deuterium. There can be millions of them at that threshold this very moment. No doubt that one of them, by some fraction of a percent, will be the 'largest', or at least, the most massive, but again, this is not faith. This is formula.

When you are talking about something humans invent, such as God, what can't we know about him? We can invent any attribute we want, and when we invent mysterious, 'unknowable' attributes, that is just laziness on the part of the inventor.

There are real things of which we conceive but do not comprehensively know. Gods and other fictional beings are not among them. It fits the theist mindset well that you have to appeal to scientific ignorance to justify your deliberate lack of imagination. And, it is deliberate. You could as easily pretend to know everything about god as you pretend to know only a little, but if you really believed you knew your god inside and out, you would probably not fear it as much as you do.

God is one without the ability to pluralise,
God relies on nothing to sustain Him,
God does not Beget (use part of Him to create another - or pass on the role of God), nor was God born (necessary being),
And there is nothing exactly like God. (Nothing we can imagine is God).

These are all qualities you have arbitrarily applied to the fictional being of your choice. They mean nothing to us and you cannot demonstrate the reality of any of them. You may mistake these as axiomatic fact, but don't expect everyone else to share in your errors.