The paniers on the legs for instance sound like they'll take about three minutes for you to figure out they won't work cross-country
Agreed. I'd be happy to be proven wrong, but I think that has very little chance of working.
A shakedown trip is a good idea and highly recommended, but learning on a long tour is also possible, especially on a multi month trip. It helps if you have someone who can mail you things and that you can send things that are not working back to. Receiving things via general delivery is great in this regard.
Carrying gear will likely be one of the most difficult issues. I know that when looking into a possible coast to coast run I found a number of coast to coast runners who found even a very light backpack to be problematic and had to adjust. The two most likely solutions are to pack extremely
light or to pack merely very light and use a baby jogger.
If you pack light enough you might be able to get by with one of the larger Mountainsmith fanny packs. If you go with the baby jogger you might want to trick it out a bit with nicer wheels, better brakes, and also by removing everything unnecessary. You may find the brakes on the baby jogger are actually helpful on some of the very long descents.