There is no requirement to set up a "node" in the network. A node's job is just to propagate actions of the network to other nodes. A node does not imply baking. A node operator is not given incentive (rewards) by the network to run a node. This fact is true throughout pretty much any other blockchain. Though if you want to bake, your baker software must communicate with a node.
As far as registering before having a full roll, while you may register your address as a baker at any time, you will not be given rights any earlier prior to accumulating a roll (8000 XTZ). So there is little reason to register as a baker before you have at least a roll (total of your own + people who delegate to you).
So to answer your question, yes, you will need at least a roll to bake.