@fireblader4 use a DC-DC step down converter to turn 14V into 12V for the strip. The Arduino can run off of the 12V using its on board regulator as long as you don't power anything else off of its 5V rail, or use a second step down converter to make 5V for the Arduino.
Then buy a 2.5A or more, 12V output buck converter but be sure it will work with an input of a little less than 14V, like 13.5V.
You can power the LEDs and the nano with the 12V provided you do not have any high current devices connected to the nano 5V output pin