Advise on selecting buck regulator to power Arduino and diaphragm pump

I wanted to get your opinion on providing steady flow to a diaphragm pump. My goal is to have very consistent air flow provided by the pump. My current plan is the following:

a) 12 VDC battery. b) Buck voltage down to 6 VDC. c) Connect 6 VDC to MOSFET to provide power to diaphragm pump. d) Connect 6 VDC to voltage divider to supply 5 VDC to Arduino. e) Arduino sends digital signal to mosfet to operate pump. f) I expect ~250 mW needed for the pump. g) I expect ~250 mW needed for the Arduino.

In your experience, do I need to watch for ripple on the digital signal to the MOSFET? Will it affect the behavior of the MOSFET?

If so, would it be better to buck down to 7 VDC and send the voltage to the linear regulator on the Arduino?

I could simplify and use a linear regulator to get down from 12 VDC for everything. I'm a bit hesitant to generate that much heat in a small confined box. Have any of you used a fan to keep the temperature down with good success?

Thanks for reading, Mike

d) Connect 6 VDC to voltage divider to supply 5 VDC to Arduino.

6V in to a voltage divider that is supposed to provide 5V output is too little. You need 7V in to get consistent 5V output.

g) I expect ~250 mW needed for the Arduino.

What is the Arduino going to do with all that power?

Have any of you used a fan to keep the temperature down with good success?

Since fans were first invented, that is what they have been used for.