Yes you should put screen and back protector. And if you want the side to be protected, put bumper instead of a case. You don't want to end up noticing scratch on your screen everytime you look at the screen don't you?
SGP has a clear and thin type. But after awhile the protector itself will get scratches, but yea it's the purpose of it. And i think the maker does actually have this intention, so after a while you need to buy it again.
Zagg has also clear type, but it's thicker and stronger. So if you want to put a case later, just buy the the zagg invisible screen protector. But if you want your iphone to be naked all the way to the end, they also sell front and back protectors in one package.