64 Dart 270 Rewire Questions

First, get the wiring diagrams and FSM for your car, try mymopar.com to start with. You're not trying to reinvent the wheel here, the factory system is a good STARTING POINT.
Then do a search for the MAD ammeter bypass.
Then decide if you're going with electronic ignition and voltage regulator; and if you're upgrading the alternator, upgrade the wiring for that, too.
And don't skimp on your grounds.
Decide if you're upgrading your headlights to a relay system.
A relay box won't be a bad idea if you're planning on future updates/additions ie stereo, door locks...
Then sit down with a paper and pencil and draw it all out with the additions you have decided to make, and have all the extra parts IN HAND before you start.
It all begins here, an evening or three with just you, a beer and the "Search" button. Good Luck.