I'm not the OP but I have worked at CP for almost 20 years, so I thought I would address your questions for you.
Early Entry: Enter the park ONE HOUR before the general public to ride Maverick, Millennium Force, Iron Dragon, Raptor and the rides in Planet Snoopy! Weather or maintenance conditions may make rides unavailable. (Got that right off the site: http://www.cedarpoint.com/public/park/resorts/index.cfm )
Weather: Typically mid-June brings high-70's to low-80's temps without much humidity yet. But it can still get quite cool, especially if it's overcast or you stay into the evening. You'll want to be sure to bring a sweatshirt with you, just in case.
Waits: Weekdays are obviously the better choice for visiting the park. I won't lie, by the times schools are out in mid-June, the weekends are getting busy. Not as bad as July, Aug, Sept, and Oct, but you will most likely be looking at 45 minutes to 90 mins. waits, depending upon the ride.
I hope this helps and have a GREAT visit!