Yes, the non-raw values are always reported with higher meaning better. The raw values are the raw measurements/counts and they each mean different things.

Is the number the percentage of a max 100%?

You did the right thing by replacing the Seagate ST2000DM008. I do data recovery professionally and that's not one of my favorite drives! Lots of issues IMHO.

No, sometimes it's in the 0-200 range. I believe the device always reports the maximum and minimum possible values.