M.W.
My brother & I are four years apart & we've always been very close. My eldest is 4 1/2 years older than my middle & they are best friends. They're always together, infact (we homeschool); they play together, watch TV together. I'd say they spend more time hanging out together than they do apart, definitely. They argue a bit, but nothing more than what you'd expect of any siblings. They're very close; if you ask Madison who her best friend is, she names her sister.
Your little one will be a big help to you! He's old enough to be a helper and young enough to feel really important & special while doing it. He'll probably have some jealousy or issues adjusting to the change, so be prepared for some acting out of some kind. Nothing major, but he'll need to feel like he's still super important & loved; some alone time with Daddy at Chuck E Cheese or something like that once the baby comes.
You'll have a great time watching your boy turn into a big brother! Congratulations!