I have made recordings in that big room and they sounded good - but I prefer the control I have of playing in a dry room. Plus it's actually harder to play in a really ambient space.
I had the walls 'dry lined' - so there is a lot of rock-wool behind the plasterboard now - and there is an under-floor heating system. It was neccasary because of the heating (more than the extra sound isolation) - although I guess that helps reduce the noise that escapes outside the building.
I tried every polar pattern setting on the AKG C12s and the one I liked is almost totally cardioid. I never change the setting for different situations or songs.
Not that I have encountered, I just follow whatever sounds best to my ears. I never really liked the traditional positioning of overheads.
I can't say I've had that particular problem. Do you play with your thumb on top of the stick (like French grip) ?
I have had 'tennis-elbow' problems - and there have been times where I have had blisters until I have developed calluses. There have been some painful times on stage !
cheers
Gavin