If I do I do and if I don't then I don't

No, people are the most advanced animals on the planet, skin, bones, muscles, organs that's it. The concept of a soul is a religious crutch. It does not exist.

Why, exactly, do i need one?!

Soul. Essence. Spirit. Energy. Whatever you call it, yes, I have that. And I believe it continues after our body/shell ceases to function. Death is just a passage way.

For humans to have a soul, all living things would have one too. That makes heaven pretty crowded.

A soul, human or otherwise is a meaningless concept that is unverifiable, unfalsifiable and has no utility.

Do identical twins have half a soul? Do dizygotic (merged fraternal twins) people have two souls in one body? The only aspects that might distinguish a soul is it's personality and memory. Outside of one's lifetime, what would be the meaning of that personality and its memories?

I don't know. I thought I did, even after I left Catholicism. But, I guess I still have a lot of stuff to ponder.