You can leave WiFi and the GPS on all day long as long as your GPS isn't being used by an app. And you dont have any apps sending/receiving data over WiFi a lot.
I typically leave Bluetooth, 3G, 4G, WiFi, and GPS off. Stops apps from doing what they want if for some reason an app defaults to its original send/receive data schedule.
You dont have to turn on any of those radios to text or talk on the phone. 3G, 4G, and Wifi ate only for data. If you need to navigate using Telenav or Navigation, you must have GPS on and coupled with 3G, 4G, or WiFi.
Yes, HTC has toggle switches for all the radios which allows you to quickly turn on/off those radios. You must add the toggle switches to a homescreen. I put mine on a screen close to my primary screen since I like to leave my radios off.
Want to download digital voicemail you must toggle 3G, 4G, or WiFi on in order to download the messages.