Electrical panel question

I think I'd put the new panel on the interior to the right of the old one. I'd get a new meter socket and a disconnect, all installed and wired to the new panel on the exterior of your home. When you were ready to cut it over, I'd shorten the feed conduit and install a junction box below the existing panel and stub conduit to the exterior and then to the new disconnect. Splice the main feed conductors in the junction box and run the new conductors to the new disconnect. Then start transferring the branch circuits from the old panel to the new panel.