Are the stock fans enough for the Define r5?

You didn't even provide your SPECS so we have no idea how much heat you'll generate. An FX-8350 overclocked with 2xR9-290X is a lot different than an i5-4590 + GTX960...

Having said that, in my experience it's rare that you need much more than a single intake and exhaust fan on a gaming rig (not counting the PSU fan which exhausts heat).

I did some testing by CRANKING UP FAN SPEED and discovered it didn't make much difference on the CPU and GPU temperatures.