6.5 should do it.

Some take 6 (which is what the manual calls for)

Some will take up to 7.

I always split mine so that the level was just below the top hashmark. 6.5 was the magic number for me.

You'll be just fine with 6.

As for the oil, MaxLife ain't a bad oil. Certainly can't hurt it by using it and changing it at the appropriate intervals.