There are few main differences between the mini 5" and the larger 10" reactor. First, the mini is designed to either run carbon alone or a mix of GFO and carbon. While it might be possible, we don't suggest running GFO alone because the reactor is a bit too short to get it to tumble properly.
While the larger reactor can be used with different volumes of GFO and carbon by sliding the foam disk up and down, with the mini we suggest packing the small cartridge full which will prevent issues from the carbon and/or GFO tumbling and creating unnecessary fines.
This means you can add around 3/4’s cup carbon to the reactor or a mix of one half cup carbon and a quarter cup of GFO. You will need a tool like a screw driver to pop the top off, add your media, replace the foam top and both plastic lids and you are ready to go.
There are two ways to go about installing this small reactor which is probably heavily dependent on your spatial constraints. First one is to cut all the tubing very short so the pump basically hangs right off the intake and then place the valve right on the output.
This produces a small, compact reactor which can just be set down anywhere in the sump. When it comes time to replace the media you can just close the valve and flip the pump up to stop water from spilling. Then, take the whole thing to the sink (which is probably the cleanest and easiest way I have ever changed media in any reactor.)
As to the flow rate, you can adjust it down if you like but since this is a closed loop where the carbon and GFO have many passes to capture the contaminants, the exact flow rate isn't a major concern. The flow rate will slow and contact time increases as the cartridge gets clogged with tank debris which makes it kind of self-regulating.
If you don't have room in your sump you can mount reactor on the wall or inside your cabinet and use longer tubes to submerge the pump and the reactor output.
We do have a couple quick tips on silencing your reactor. Coupled with a Colbat MJ these things run dead silent but you can get some noise from the pump vibrating against the reactor or something else in the tank like the side of the sump or from vibration transfer to the tubes and something they touch.
The easiest one I have found is these food grade silicone mats. just cut a piece and place it between whatever it is vibrating against or even better just wrap the pump with the silicone and zip tie it in place.
For a more flexible install and zero noise transfer you can pick up some half inch ID silicone tubing as well as these 1/2" mur-lok stem adapters. I have been using silicone pretty much anywhere I can these days.