If I read you correctly you intend to fully flood your loop at 50m as a practice? I haven't much experience but it sounds extremely dodgy to me. I have practiced dealing with a loop flood...but that is under controlled conditions at a depth that if all went pear shaped I could still get myself to the surface without too much drama, and didn't involve actually filling the unit to the brim and making myself extremely negatively buoyant!.
My understanding was that the practice was to build muscle memory and motor skills rather than placing yourself in potential danger.
I'm sure an instructor will be along to put me right shortly though
Apart from that it all sounded fine...