Re: Left hand technique during chords
As a fiddle player, do you play any of the Bach Sonatas and Partitas for Unaccompanied Violin? Have you had any teachers try to walk you through them? There are some really killer 4-note chords in there, and they won't all fall into natural hand positions. Some of your experience on the violin with the hairier chords in there should transfer to the mandolin.
As already mentioned, you should try to form your chords as naturally as possible while retaining the same hand position and finger orientation as for your single-line playing.
However, you'll find some chords that are just monsters to play, and you'll have to break the rules. For those chords, anything goes! Mike Marshall covers this in vol. 2 of his instructional DVDs, and he gives us permission and justification for breaking the rules when it becomes necessary.
So try to retain natural position as much as possible, but don't get too neurotic if, after a lot of trying, you can't find a "natural" position that works.
Adult-onset Instrumentalist (or was that addled-onset?)