Yes I have a return line directly to the Res it's 1/2" & my lines coming out of the Res to my buckets is all 3/4" & my grommets are 3/4" Hydro Flow & 1/2" Hydrofarm Top hat grommet to the Res.
I agree wrap ur buckets,& most def invest in a chiller,I'm running 4 buckets 17 gal Res & im running an Elemental 1/4 hp it's good for up to 40 gals max.if your not running chiller your almost guaranteed you'll get root rot.clean set up
Dissolved Oxygen is key in RDWC,mass aeriation in your Res & buckets.& keep your Nute solution around 64-66 degress & you won't get root rot,Oh & run Cannazyme by Canna Nutrients it's the shit for the Root Zone.
No I've ran 4" stones,Air diffusers sit @ the bottom of the bucket & evenly distribute micro bubbles 360 degress for mass roots.if you notice in the pic the bubblesz