Has anybody used the Fractal Design Core 3500 case? It seems to be a scaled down Define R5, with no door and all 140 (or 120)mm fans. The top grills are always open - this may be the thing I would be worried about. The Define R5 has room for 8 hard drives, which is just nuts, while the Core 3500 has room for 4; along with the same 2 SSD spaces behind the motherboard. More than enough drive bays.
The front edge intakes look a bit restrictive, but maybe they are still big enough to work well, and having the bottom (filtered) intakes do more "work" may be a good thing.