With the one-step approval process: If I open a job, and manually upload art, the status shows "waiting for approval". Has it already sent out a proof for approval to the customer?

Yes, with the one-step approval process, the proof is sent to the customer as soon as the artwork is uploaded and tFLOW has processed the job.  The two-step approval requires an internal approval before it gets sent out to the customer, so it would let you approve the job before your customer is alerted that it is created.  However, you can set the attributes of the job before uploading the artwork by clicking the "Add Job" button which will open up a dialogue box where you can set all of the parameters of the job before creating it.