It's really up to you, it would depend on how much you want to battle. You can play without battling a whole lot, but obviously the more you battle, the more currency you get and the more Pokemon you can buy/obtain. I probably only battle 2-4 times a week on average and manage to get by alright.
You would probably make enough if you just connected once a week on the weekend when a lot of people are online to battle. This Saturday you actually get double stars for battling, so if you popped into our xat
chat on that day, you should be able to find 4-5 people you could battle all at once, and you would make enough stars to keep you going for a while!
It's not recommended, but it is possible to play the game without actually battling at all. Hope you decide to join! :D If you need any help, just let us know!