For those interested to know how I finally did it.
I initially used Gelid fan. Finally, I thought the chassis top was getting a bit hot, and the fan might not be enough to handle the processor. I bought a Dynatron K199 instead, and just installed it right now. Seems the heat on top of the case is about the same. Will just leave the Dynatron as it is. BTW, I have a Gigabit metal switch directly on top of the 1U chassis, maybe that's why it's a bit hot on top. But I have my Gelid fan running for over a month, with the switch on top, without a problem.
Then there's the other issue of how to get it silent. If I were to use the PSU that came with the chassis, it will be too noisy. I had to improvise. I have a pico psu lying around from old mini itx case (industrial type). I gutted out the psu board. I used Epoxy on the standoffs, and had it mounted on the chassis. Screwed the pico psu on the standoffs. For portability, and compactness, I used Velcro on the power adaptor, and put it inside instead of outside the chassis. Used Velcro on the SSD as well. I manually traced the pins on the chassis, and only got the power switch, reset switch, power led, and hdd led working. I don't have the network activity led functioning. Although getting the network activity led will make this DIY case/ Firewall look awesome. As for the back, I don't have I/O plate, so I had to manually file
the holes. I could have cut out the whole rectangular section, to put in a backplate, but this motherboard of mine is missing backplate too, so I had to file the holes, cut the rectangles manually instead. Comments on how to improve this is more than welcome
I forgot to mention, I used this as a home firewall. I bought a dual port Intel NIC card, and bought a riser cable to fit it on the chassis. Though I feel my riser cable is too wide, 16x whereas a x4 riser cable could probably been better for air circulation.
Again, if anyone can offer how to get network activity led working, I'm happy to hear it.