You’d have to reconfigure those districts based on population. They’re not exactly “fairly” drawn as it is.
Not necessarily. The U.S. House is based on population, the U.S. Senate is based on equal power of all 50 states. Both bodies are popularly-elected. You could replace an appointed court with an elected court and keep the current federal circuit districts completely intact, as long as you had provisions for all nine judges to run in at least one of them.
BTW, this would force the judges to "ride the circuit" and meet with the locals courts in their district, which they used to do regularly in the 19th century but currently ignore "their" constituency.
They'd probably be a push to redraw the map anyway, just because the current districts are so uneven (the western states get their own giant district with about 12 states including California).
But I'd push for the district lines to be redrawn so they each hold several states but are more-or-less equal in area (square miles) of the continental USA. Not sure what we'd do with Alaska and Hawaii though...