1. Currently I connected my LED strip without a resistor, but do I want to add that in the "end product"?
2. I saw a video about connecting a 12V LED to the Arduino using a TIP122 transistor, so the LED is controlled by the Arduino, but uses the current & voltage of the battery, is this the way to go? I also saw a "Step Up Converter" which maybe could change an Arduino pin output to 12V but I think this will ask too much from the Arduino.
3. I read that using more than 12V as input for the Arduino could lead to damage, since the battery could potentially output 13-14V this is bad. I could just use a usb car adapter to power the Arduino, or is there something easier?
4. Do I need to add more resistors? Maybe for the 12V light (with 2 positive sides)?
5. Also this is for one side (turning signal) obviously, if I want to support both sides, is it better to do this with another Arduino, or should this be no problem with one? (Sure I need to change the program but that's no problem for me)