Make that list and make it fast, remember showers are a timed events so you don't have time to waste.
Invite only those that can really help you. I know its sounds like you are being desperate of snobby. But in reality a baby shower is a celebratory ceremony of supporters, so its a good idea to surround your future child with those who will stand by you when you really need it.
KISS - keep it simple, along with being pregnant you do not want to stress yourself right before you give birth. The number one way to keep it simple is give everyone in step two only one thing to do. I know you are reading this and saying "this guy is out of his mind I want family to come and just enjoy." In really if that's all you want them to do that's how its going to be after you have the child, its your choice but choose wisely because afterwards its too late.
I have seen countless showers with everyone at the helm and seeing the mother to be glow and i have seen the opposite and sometimes i have to go home to fight back the tears.
Show everyone love that comes out to appreciate whats the most important thing to come into your life.