I don't know if someone has corrected my earlier post. I was wrong about the video and production speed. The video was played at normal speed. Which means that's how the robots are moving at the moment. Once it's confirmed working fine, it will work 10 times faster.
Also if a particular step is done by manual work, the whole production line can still achieve 10,000 cars per week, as long as that step can finish in 1 minute. Or if it takes 5 minutes to finish that step, they can have 5 sets of manual workers to do that step. Anyway, I wouldn't be concerned if there are some manual work in the line.
Turning from 5,000 per week to 10,000 per week will not need to duplicate the production line. They just need to double part of the line. Any robots/stages that can finish their work in 1 minute don't need to be doubled.
There will be no humans doing work in or for the model 3 line to slow it down. When it is up to speed, Musk has said the humans will be banned. It wouldn't be safe for those fragile life forms.
There could be manual work being done now, but the line is not running at speed. Once it does, human involvement would mean failure.