1. Can't "repeal" Citizens' United. It's a constitutional decision. But the coverage formula for Section 4 of the Civil Right Act could be revisited and passed into law, and that would bring back preclearance.
It's also possible for Congress to pass a campaign finance reform bill that addresses the Citizens' United arguments, and then relitigate with a more favorable Supreme Court.
And ah, there's the rub. Can't do anything worthwhile in constitutional law before fixing the Supreme Court.
2. My first effort would be to create about 30 new states, and then amend the constitution to fix all the various problems with it, and as part of the amendment, the new states would be retracted. No new states could then be created without an amendment to the constitution.
We could get rid of all of the crap plaguing us right now. No more stupid unitary executive theory. No more disrespect of independent agencies. No more Electoral College and unequal representation in the Senate (or at least less unequal). No more weaponization of the First Amendment against unions. No more second amendment.