S100fs - have problem getting focus spot on

I have a problem getting my focus right. Viewing through the EVF is a pain, the image is too small and I can't tell if the image looks sharp enough. Anyone having the same problem?
I have a few questions to ask:

1. Do you always set AF assist focus ON most of the time. I find the light emitted annoying so I had it OFF.

2. Which focus setting is best for focusing ie. multi, centre or spot? I can't seem to get it right even after trying all modes.

3. Manual focus, don't even try it unless you like unsharp images. How to I get it right?

Thanks, I am still new to the camera. Hoping to get some tips from F100fs users.