Controlling rc servo motor using motorcycle battery


I am using an rc standard servo to actuate the clutch lever on my motorcycle using an Uno. I am wondering the easiest way to step-down the voltage to exactly 7.4V to meet the servo's specifications. I need all the torque available so having a low tolerance level is a must. I was looking at getting a variable buck converter - would that work? The motorcycle battery will be between 12-13V. I am also using a 7805 TO220 to regulate arduino power, so any input on that would be appreciated as well.

Second issue is regarding the actuation of two solenoid valves from the arduino. I am using two darlington NPN's (TIP120) from the arduino. The valves are 12VDC and 2.5W, so amps should be around 200-300mA. Would this setup suffice for my project?

Thank you.