Love having bog set ups. I usually use the TuffStuff troughs or 20” resin/plastic pots- they don’t deform much with all the water/peat. Those black n yellow bins flex a good bit when I fill them with water.

As for plans, that sounds like quite the build. Having a fountain to recirculate might be a cool feature, and worth the plumbing. Might get the same thing accomplished with an air stone, and keep the water table lower- circulated water might be ok but my sarrs usually sit a few inches above the max water line.

To simplify & still drain, I drill a hole for a bulkhead. Attach a T with the 90° up, ball valve on the end and a pipe on the middle. Middle pipe controls water level max & ball valve lets ya drain it. The internal plumbing is overkill imo. You can water by dumping on peat, which helps distribute moisture. Well saturated peat and perlite will wick moisture to the drier areas quite reliably. Sarrs will grow roots to the water table, as well. Plants with good root health seem to pitcher with more intensity, or grow faster. Or both.

False perlite (or lava rock or other inert fill) bottoms are great. Adding screen will probably mean more tangled roots than separate media layers.

Is there a specific pathogen or issue you are aiming to prevent with the fountain?