Well for a start I think it absolutely matters "what God or what religion". (your second sentence above). You cant say "just if there is one".
Because what "kind of god" exists (if there exists one) determines what the outcome of this would be.
Just an example:
If a Christian God exists then most probably it doesn't actually matter what you say or believed. If you didn't believe in Jebus in your lifetime, you are in trouble.
Also your other questions depend on the god that exists. For example i cant tell you if "God" understands my reasons when passing judgment unless we can agree that we talk about a God who is capable or incapable of doing so. If we agree on such a preposition, then the question becomes obsolete however.
You get my point?
Another problem, one that philosophers have struggled with for eons, is that "god" is a nedulus concept.
What exactly does one MEAN when they say god? What attributes should we expect this god to have?
If you randomly assemble a group of theist's, you may well get several interprations and arguments about which concept is correct.
Theist's know they cant all be correct; so they rationalize their personal belief to be the true one, at the total exclusion of all others.
It makes me think of a Homer Simpson quote:
"Suppose we have chosen the WRONG god, every time we go to church, we are making him madder and madder" :)
This just illustrates the sillyness of it all to me :)
*Hi five on that one!.... wait!!!! :-(
I would be pretty shocked at first, angry too. but i would eventually accept it, but i would never bring myself to worship it/them.
I can't help but be reminded of my favorite quotes:
“How gullible are you? Is your gullibility located in some "gullibility center" in your brain? Could a neurosurgeon reach in and perform some delicate operation to lower your gullibility, otherwise leaving you alone? If you believe this, you are pretty gullible, and should perhaps consider such an operation.”
~ Douglas R. Hofstadter
If there's a god, it is bat-shit crazy or else how is described by the devil in Devil's Advocate, an absentee landlord. I see little chance for such an entity to exist, given our universe. If shown to us, we'd probably see it as an advanced life-form and little more.
In other words, many of us have outgrown the concept.
I would take the late Christopher Hitchens' lead and hope that whatever this "god" is would prefer honest disbelief to dishonest belief "just in case".
Live a good life. If there are gods and they are just, then they will not care how devout you have been, but will welcome you based on the virtues you have lived by. If there are gods, but unjust, then you should not want to worship them. If there are no gods, then you will be gone, but will have lived a noble life that will live on in the memories of your loved ones.