It's quite unusial to build an infrastructure from scratch using OpenWISP without a strong technical background. You’re in for a ton of nuances like load balancing when connecting real users, DNS and all other settings and, yes, logging (sorry, I keep bringing it up because it’s the backbone of proxy farmer security).
I'd strongly recommend finding a skilled network specialist to discuss all details before launching and who can assist promptly during operations.
Regarding your question -- the US is a world top location. If you provide quality proxies, demand will be there. The challenge is keeping up with the need for new proxy ports.