I have an idea to build a product using portable WiFi Safe.

I have an idea to build a product using portable WiFi Safe. Was able to use Arduino/Sonoff SV and build a working POC. However on this kind of hardware project, my question is how do I take it to next level. Specifically
a) How do I design the final version that is energy efficient, runs on battery or ensure I am on the right track (first time user).
b) How do I get prototype built. Are there shops in US who can assist with it

Any assistance appreciated from someone who has been through this path.