bindog wrote:
I'm also focussing on muting the low e string as much as possible when playing 5th string barres in general.. How important is it to do this properly and not either fret it or let it ring open?
This depends entirely on what you're playing and the effect you are going for. I think it's important to be able to be able to do all three (mute, ring open, or fret) when you want to.
I would focus on the muting for now. Also, realise that if you were to fret the note on the low E, that you will be playing the fifth of your tonic, but an octave lower. Say you are playing a D major barre chord at the 5th fret, and you accidentally fret the A on the low E, well, A is the fifth of D, so it will still be in key, but with a different feel (because your root note is no longer the deepest in your chord). If you were to play the low E open though, it would be very different, as you would then be adding your flat 7th, and playing a D7. Muting the low E will play the d major you are looking for, with your root being the lowest note.
If you were to play a C major barre chord on your third fret, then , if you fret the G on the 6th string, you do the same thing as when you fret the A whilst playing Dmaj...you create an inversion by playing your fifth (G is the fifth of Cmajor) but an octave lower. In this case, playing the 6th string as an open E note is also going to be in key, because E is the third of your Cmajor chord and is already fretted elsewhere in this chord, you're just adding a lower third.
Sorry I am rambling, but I hope I am making sense.
My point is that all three approaches are correct if you do what you're planning to do, and no approach is correct if you do something different to what you're planning to do.