About fireflies,... I'm not sure if this is the solution you are looking for, but I've had my share of frustrations how to get rid of them and at the end I found that I had better results if the sky reflections were not produced by a HDR/EXR file but rather with a regular bitmap.
So now I have the habitude to seperate the two like so:
I have a sky with a JPG/PNG/TIF , with compositing tag to enable for background/reflections/refractions/mask
and a sky for lighting with HDR/EXR file with compositing tag to enable for GI and shadows
Again, I'm not saying this is the better way to go, but it works for me...
Cheers,