Just browse this topic..... or:
https://www.dan-cases.com/dana4_hof.html
With that GPU block I linked, there is space for a 120mm rad next to the GPU on the GPU side. I could hang the pump on the side panel with tirewraps (on the inside) above the CPU block and fit the reservoir under the PSU.
I'm in the process of trying to do the same as you. I found this rad:
https://www.xs-pc.com/radiators-tx-series/tx120-ultrathin-radiator which is just 20mm thick so I can fit a Noctua Industrual on top of it.
The issue is that a pico PSU requires an external power brick, which I don't want, plus it only goes up to like 200 watts.
What are you thoughts?
That radiator seem like a great contender for this case, I am not too familiar with XS myself.
As far as the pico PSU there are various that I have come across myself, I feel like a pico PSU is a must for a custom water cooled in this case because of the potential space savings. One issue is that I don't own this case and it is difficult to judge how much space there actually is.
Of course it ultimately comes down to your build and your power needs, some people can do just fine with 200 watts but I presume that your not one of those people. I recently picked up a 400 watt pico psu from HDPLEX, I intended to pick up the 160 watt one but they were unavailable. I've been very happy with it and running it with a spare laptop charger that I had. This is of course powering my low powered server.
Some other thoughts are that on my primary rig I have a I5 7600K and a RX480 overclocked as far as I could take them, when measuring the power consumption at the wall at idle i pull around 90 watts, under a heavy gaming load I pull an average of 300 watts with momentary peaks at times near 350 watts. I have not tried my 400 watt psu with this rig but it should be just enough to handle it, apparently the psu has some head room above its advertised 400 watt rating as well. Another thing to note is that you are also limited by the wattage of your power brick so picking up a quality brick is also key!
It looks like my psu could potentially fit under neath the graphics card area and adding some custom built, custom length cables would be a great idea to match