Believe Nothing.

Should we believe in what we cannot see? Mate, I don't believe in half of what I CAN see.

You say no-one's ever seen God and ask whether it should stop anyone believing that God POSSIBLY COULD exist. It certainly doesn't stop us believing that it POSSIBLY could exist. However that doesn't mean we should go beyond that into the blind certainty that it does exist in the absence of or despite evidence.

I find it interesting that you imagine God as being some kind of humanoid life form. Would it have a mouth? Why... to eat? to eat what? Would it have an anus? Does that mean it extretes? And the slightly more disturbing questions what and where?

I get what you mean though about attempting to imagine multiple dimensions above and beyond the normal three. My brother and I used to play six dimensional noughts and crosses with one another, it made me start feeling dizzy after the first few games trying to imagine the directional relationships in all six dimensions.

So basically you're asking is it crazy to believe in something you can't see and/or imagine. And the answer is...

Yes.
It is crazy. You can accept the possibility of it, anything more certain is self-delusion. True wisdom is knowing that we know nothing (thankyou Socrates).