Is a 650w PSU enough for this build?

Yes. for any Single GPU setup 650w is the perfect middle ground taking in consideration of trying to power any other future components you wish to add into your system. if you want to go SLI or Crossfire in the future then consider an 850w.

Yes a 650w is enough. Make sure you get a well-known brand with a good quailty unit. 

I'm planning of getting a tx650 from Corsair

or a HX650 if i have the money