Drew's Doser is the already assembled version IIRC, however the one time someone pointed it out from BRS (I think) I could not find it on their website.
I went with DC because at first I thought about adjusting the voltage to suit my needs, but later saw it wasn't necessary due to not running the pump continuously and simply run it at max for a set time (on a timer). Also DC pumps faster (more RPMs on the motor) as a result you don't have to run them as long, although I think they are a bit noisier (but you're going faster so yeah!)
Tubing, silicon, and go with the largest size the pump allows so I don't need to leave it on as long, and you're set.
No other casing options or anything, simply soldered the leads to a 12v wall wart I had laying around to the pins on the back, and I was good to go. I have my timer go about 30 minutes a day to push about 2 cups of 2-part solutin (at half strength) into my tank.