If you didn't already have an instrument, my first piece of advice would be to get a smaller box. Its difficult not to drown out everyone else with a 120 Bass. They are inherently loud, but the more subtle players can get away with it.

Some people worth listening to, if your interested in Irish or celtic music are Phil Cunningham, Karen Tweed, Seamus Mehan (I don't know that he's widely recorded but look for The Temple House Ceili Band). I've heard Mr Pirt who has posted above a few times playing with his band 422 and he's definitely another one for this list.

Try to keep your touch as light as possible and use the bass sparingly. When I was in an accordion band we were thought to use the bass to bang out the rhythm oom-pah-pah style and I think that sounds pretty awful now.

I own a 72 Bass Paolo Soprani myself, although I haven't played it for years.