E-5 low light picture (exterior concert)

Hello,

I'm taking my E-5 with 12-60mm, 50-200mm OLY and 30mm f1.4 Sigma at a concert at night in a wonderful exterior (Rosh Hanikra). The concert will be minimalist one single performer and a piano. Certainly not a lot of lights.

I will also have some times to catch sunset insides grottoes open to the sea.

Things is, i always add troubles with setting and low light conditions.
I always ended with blured or over iso'ed pictures.

I'll be glad to have some tips... Unless Olympus is really not feed for this.
I still have an iphone you know.

Bernard