First question - Yes, that's right, EW is what you'd mark down.
Second - I'm not sure. I haven't read much about an ovulation dip, I think it's one of those things that could mean nothing. No way to know until later.
Third - Empty circles come from if you either check something like "fever" (which would indicate that your temperture is not normal) or if you temped at a different time of day than normal. So if you usually wake up and temp at 6am and one day you slept in until 8am, that will show up as an open circle (because that *can* affect your temperture).