Were in the process of building one now, using Yetter 2996 coulters with knives. We are 12-36 so were going to try using 11 coulters and use 1.5 rate on the outsides, if we don't like it we will go to 13 coulters and 1/2 rate the outside. Seen it done both ways, heard good and bad about both so were going to see for ourselves. We are in some pretty serious hills so gauge wheels are a must, but I think theyre a good idea anyway. Ours has a 500gal tank on the bar and a pair of 300gal saddle tanks on the tractor.  Hydraulic centrifugal pump with 4 sections and applied rate controlled by a Trimble FM1000.  Planning on being able to put on around 50gal/acre if needed.