How are you interfacing with these things on Windows 7?
I've installed the Hangouts Chrome Extension/Chome App. I can call for free (using a headset) very easily straight from these little apps. I've also had to set up multiple Chrome Profiles/accounts so each one can run the Hangouts Extension separately.
You are right though: There doesn't seem to be a way to add contacts from these apps. For that you need to use
https://contacts.google.com/ which will sync with the Hangouts app after a few minutes. It's not convenient, but it's free. And once the contacts are actually in your contact list, they're easily and quickly searchable from the Hangouts app.
I'm on Windows 10, but the idea should be pretty much the same. I've been doing it more or less this way for several years now. I haven't paid for phone service (except an occasional 30 days on a pre-paid plan while traveling) since probably 2010 or so.