I've looked at the Circle of Fifths at different times over the years and thought "so what?" but that is because I had no-one to explain it to me in a logical & practical way.

So, about these chords I can use: any suggestions for some really nice progressions, given the limitations? Or do I just use the same progressions you have suggested by using the roman numerals and ignore whether it is in fact exactly the same chord that you would play on a guitar, where you have a choice, i.e. with accidentals whenever you want?

I mostly play Celtic, folk, early 20th century popular, etc.

BTW, the info I read on the circle of fifths is here:

Theory on Tap: Lesson V, Circle of Fifths

http://www.scroom.com/mus_lessons/tot.5.html

It was a Mudcat recommended site, from another thread quite a while back - I forget which.

Helen