I answer the substrate swap question a lot so I wrote it all down:
-Unplug heater
-Start draining tank halfway
-Remove decor
-Fill bucket with tank water
-Unplug filter and put media in bucket with tank water
-Net fish and add to bucket with media
-Drain rest of the way
-Use a container to scoop gravel out (or if you have a wet/dry shop vacuum, use that, it's sooo much easier)
-Rinse substrate (recommend using pillow case trick)
-Add Substrate
-Add base decor
-Add water halfway
-Plug heater in
-Add rest of decor/plants
-Fill up rest of the way with water
-Treat water with conditioner
-Drip acclimate fish
-Set filter up
-Net fish back to tank after drip acclimation
The pillow case trick is the slickest thing I've ever learned. Get a clean pillow case. Dump 10-15lbs of sand in it at a time, stick your garden hose down in the case and stir the sand around with the water on. Keep doing this until the water that is running out of the bottom comes out clear.
As far as bottom dwellers in playsand... I have no issues. I have 5 geos (earth eaters - aptly named too) with playsand that constantly scoop up mouthfuls of sand and spit it all over the tank. I have no issues with it clouding up or being murky.
Edit: I also have cories, a clown loach, upside down cat, and loaches that don't stir up the sand either.