You can use the Hangouts dialer app to make calls, but I'm not sure you can use it to receive calls. You can use google voice to make and receive calls if you have a number. Otherwise, no you cannot use wifi to make/send calls as usual.
WiFi calling is available via apps and also rumored to be added officially by Verizon this summer to select markets and handsets. Extenders do not work well with 4G phones nor Advanced Calling, since AC requires 4G and extenders only work with 3G. OP should save that $250 dollars.