Depending on the age of your place all new outside spigots are usually tee'd off before your pressure regulating valve (PRV). This is a good score, just ensure the line does not freeze!

Good for you that you are still ordering the pump.
RO membranes work best with a minimum of 60 psi

Not saying this is it, but I have one of those and my pressure would be up and down, whether it was on or off. I found that the waste water was always running and that led to finding that the waterline connection on the RO part, not being tightened and air was either being sucked in or pushed out so the pressure was always low. Tightened it back up and it worked great.