What if I had something like this where I had a 10K pot? I don't know though that value I would need for R5. If that would work do you have any suggestions.
I'd put another resistor on the other side of the pot as well. Basically you're creating a resistor divider chain so that the voltage arriving at the gate is in the MOSFET's linear region. The exact values will depend on the MOSFET - look at the curves on the datasheet.
What kind of values should R6 and R5 be? I am not sure how to calculate it. The LEDs will draw 320mA per hour and I was thinking of using a https://www.sparkfun.com/products/522 . I will need to cut the total current to 200mA.