A couple issues come to mind from your question:

- horsepower  Our 6000 and Pluribus units generally take about 10-12 hp per row, depending on speed and terrain. To be sure of sufficient power to run at the forward speeds you will like run in KS (8-10 mph) I would figure 12 hp/row for the row units x 12 units = 144 hp.  In addition there is the hp required to pull a full Montag cart over at times soft wet ground. In addition there is the 30-40 hp required for the Montag cart's air fan to convey the fertilizer.  Overall with a JD 7730 I think you are going to be a bit short on hp to run 12 Pluribus or 6000's and a full Montag cart and run the cart fan at the same time.  You could probably run 12 rows with say liquid since a liquid pump takes much less hp than the air cart fan. However when adding a nh3 tank behind the Montag and you are definitely going to be short of hp.

- lift assist is going to be required on that setup - or a lot of weight on the front of the tractor. The Montag has most of its weight on its own wheels but it does put some additional weight on the 3 point toolbar.

- making essentially a 2nd quick change toolbar behind the first makes the change easier but also moves the cg rearward making lift assist more of a requirement.

- the Gnuse hydraulic top link is a huge help in running the Pluribus or the 6000 on a mounted toolbar. The hydraulic link allows you to make adjustments to level the bar but also to tweak it on the go - raise the nose and inch or two when approaching a wet spot or dropping the nose if you hit a particularly hard knoll.  Just allowing you to run level is an important adjustment which is not usually made with a frozen large screw adj top link and a big load.

Personally I think you have a good plan of running the 6000 in the fall and Pluribus over the same path in the spring and using the Montag cart and/or anhydrous. This is very flexible and you could probably save enough on fertilizer to pay for the setup fairly quickly on a larger operation.

Toolbar - there are several different toolbars in use successfully with both the 6000 and the Pluribus.  We have a lot of 3-point customers running Moore-Built toolbars out of Benedict, NE just north of York.

They sell a nicely made heavy duty, 3 point 12R30 vertical fold 7x7 30ft toolbar with a set of gage wheels for a bit over $10,000 last I knew. Moore Built has lift assist, rear hitch, markers, etc options available. Personally I think you would be better off in the long run just buying 2 toolbars having one setup for the 6000, one for the Pluribus. One nice thing about 3 point toolbars is that they cost only about 1/3 of what a same width pull type costs due to far less parts.

And I think in the end you will need a larger tractor to make your system work.  If we figure around 140 hp for the (12) 6000 or Pluribus row units + 40 hp for the Montag fan + 40 hp just to PULL a full cart and maybe nh3 tank up a small hill at 10 mph, that adds up to about 225 hp as a minimum.  Trading for a larger tractor may laso make the lift assist less necessary depending on final tractor selected and weight on the front.

I hope this answers most of your questions. I post the reply here rather than by email since this is a fairly general question others have asked.  I have no opinion on the JD rate controller with dry fertilizer. I do know that with NH3 folks seem to have the best experience/most uniform  row to row flow division with the ANH3 anhydrous system.

Regards,

Jim at Dawn