When I did mine I installed the new panel inside and fed it from the old panel. I could turn off the main to permit running the wires from old to new panel. The old main protected the wires and I just connected lugs to the bus bars in the old panel and ran 100 Amp wire (#2 Aluminum) to the new panel.
I then connected all of the circuits to the new panel so I didn't have to do it on change-over day.
Then I pre-fabricated as much as possible of the service conduit and meter assembly that would serve the new panel and installed as much as I could while maintaining power. I had my change-over order from the power company and a permit from the town.
I scheduled the change-over day with the inspector and the POCO and they told me I could cut the wire and remove the meter, which I did. I then installed the new meter socket and conduit, connected the new meter socket to the new panel, removed the old panel, and called the inspector.
The inspector approved the installation and called the POCO for a reconnect. I was back in business about 6 hours after I cut the power.