Hey Hooperman...
I've been playing guitar for about 25 years and about a year ago picked up the accordion for the folk band I'm in... so I feel your pain.
I just recently started taking lessons and it's hurting my brain trying to separate the tasks my hands are performing. Practice, practice, practice is the key. I remember learning to play piano in Jr. High and how I couldn't get my hands to separate... then one day I woke up and could totally do it. So, yeah, just practice and your brain will do the rest.
I can't say for The Pogues but I know for The Boggards we do a lot of our songs in D and G because that's a good key for the Baritones to sing in. Could be that C is Shane's "sweet spot". But maybe Mr. Fearnley could give us some insight.

