Basically I will use 4 of the pins to output power, and RGB values to a maximum of 3 LED strips, about 30-40 LED's.
Arduino pins do not output "power". They can only output a small current at 5V. They can power a single small led, but not much more. They are meant to control, not to power. So you will need some transistors. These can be used to boost the current and voltage to be enough for your strips. We can recommend a type of transistor once we know more about your project.
You mention using 4 pins for 3 RGB led strips. But there are several types of RGB strip. Some need 12V, some need 5V. Some allow control of individual LEDs in the strip. Some allow control of groups of 3 leds. Some only allow control of the strip as a whole. Some need transistors to drive them.
So please post a link to the type of strip you intend to use. Read the forum sticky post to find out how to post links properly so they can be clicked on. Then we can advise further how to control the led strips.
If it were my project, I would power the Nano using a dc-dc convertor as septillion says, but I would use a 12V to 5V designed for car/bike use and power the Nano through its 5V pin.