It definitely doesn't scale linearly. They had a section of the tube only several meters long for vacuum testing pods and that took 15 minutes to depressurize. It's likely bigger/more pumps would be used.
To some extent, but part of the reason for having pumps is that it removes the need to make the tube fully airtight - the idea being that it's likely to be cheaper to build a tube that is largely airtight and use pumps to deal with leaks than to build one that can keep a vacuum over time.
