Hi Simon
Welcome to the forum and good luck with your search for the right tunings for your twin eight, having a double neck 8 string non pedal myself I have decided to settle for E13th on the front neck, top to bottom G#,E,C#,B,G#,E,D,B , this tuning is based on Don Helms E13th and gives a nice E9th sound.
On the rear neck I use an A6th tuning top to bottom E,C#,A,F#,E,C#,A,G this tuning is used by Eddie Rivers and is good for Western swing, it can easily be changed to C6th Using the same strings dropping to E,C,A,G,E,C,A,G.
I find the benefit from these tunings is the fret number positions are the same 3 5 7 9 12 on both necks, you can figure out what pedal arrangements would be available using these tunings, but the worlds your oyster when pedals are involved.
I would like to see you swinging your right foot for swell on that tone/volume pedal when jumping from one pedal to another with your left foot and still figure out with your brain, where your hands are going, when that's all being done at the same time you can then think of adding leavers to get the missing notes!

Best wishes on your journey into pedal steel and good luck in finding tunings that suit your needs, meanwhile you can always use the twin neck as a double eight console and forget about the pedals for now by using the above tunings, when you figure out what slants are required for each tuning it will give you a better idea of where and how to use the pedals.
Best time to work on tunings is in bed, it's more therapeutic than counting sheep

, but it leads to nightmares

Cheers
Robert