I was just searching youtube for videos of the big time breweries to see how their mash tanks were set up and they too had mixers that looked quite similar to your design except they were made out of stainless steel and looked like there were around 6 paddles/blades/fins on the stirrer. I also want to incorporate this into my build. I'm glad you already threw this together! cheers to you! For your casing.. im sure if you search ebay for an electric box you will find one that will fit around your base with the gears.
I also noticed that the stirrers on theirs move very slow. Im guesstimating around one revolution in 45 seconds. So if you can figure out what kind of motor i need to replicate that I would appeciate it.