How do I ensure functionality of my watch receiving and making calls when I dont physically have my iPhone?

You'll only be able to do that with the cellular enabled Apple watch (not the GPS only version).

See https://support.apple.com/en-us/HT207578

You can make calls over WiFi if your carrier permit's it and also if you have previously logged on to that particular WiFi network with your iPhone.

https://support.apple.com/en-ca/guide/watch/apdc38d7a95e/watchos