I actually have an identical setup to you with the exception of the GPU where I have a 5850 instead, which is probably a bit hotter than the 660 anyways. I haven't added any fans, it's dead quiet, never had a temperature problem to speak of. I'm not overclocking, but haven't felt the need to either. I couldn't remember what the configuration I ended up with was so I popped the case open - I have the upper section of drive trays removed and the front fan blows directly toward the graphics card that blows its exhaust out the back of the case. The other fan is the back of the case behind the CPU fan that is also blowing toward the back. The ssd and hdd are in the lower drive bays and get enough airflow from the front intake and the PSU exhausting out the back at the bottom. I really like the case - I came from an Antec P180 for the last 5 years or so and 2 or 3 revisions of the Sonata before that. I think you'll be fine with the default setup, but there are plenty of options should you find you need more in the future.
i7-6700K | Z170X-Ultra Gaming | 32GB DDR4-2400 | EVGA GTX 1080 | 256GB SAMSUNG SM951 M.2 | 27" ACHIEVA 2560x1440 LED | Nanoxia Deep Silence 3 | EVGA SuperNOVA 550G2 | Win10 Pro x64.