Grand Canyon tips....
(1) Since it is your first time hiking there, take the mileage you would like to do and reduce that amount by about 1/4 or 1/3. Hiking in the Grand Canyon is VERY hard. The dust, the strong sun, and the crazy temperatures inside the canyon all make hiking difficult. Plus, the whole fact that you hike down first, then up. You absolutely need to plan on 100s in the inner canyon in June, although you may get lucky. Hundreds of deaths have occured from heat-related incidients in the grand canyon (250+ rescues per year). I would carry no less than 1.5 gallons of water per day, per person. I personally would carry 2 gallons of water per day, per person all the way from June-September.
(2) You could also consider a 2-night backpack down to Havasu Falls. It's one heck of an experience (almost 3rd-world like), but keep in mind there are some serious downsides to it (crowded, trash, etc.). It does contain the most beautiful set of swimming holes in the entire country, though. It's a few hours west of the South Rim. Make reservations in early January for this via phone. It can sell out quick.
(3) If you plan on staying at any of the lodges or campgrounds on the rim, make your reservations NOW. You'll probably find that many accomodations are already full for next June (crazy, i know).
(4) Flagstaff has any camping/hiking supplies that you'd need. It's also a cool little town worth staying in for a night.
(5) If you have time, head over to Page, where you can see "Horseshoe Bend". It's gorgeous.
(6) The South Kaibob Trail is 4x as nice as the Bright Angel trail in my opinion.
(7) The Bright Angel Restaurant is the best food for a reasonable amount of money on the rim.
(8) The highpoint of Arizona is only about 1-2 hours from the Grand Canyon.
(9) Don't spend your money on the Skywalk. It's a complete ripoff. If you want to be a true tourist, the helicopter rides are actually pretty fun (except for the fact that they have a long history of accidents).
(10) National Geographic has phenominal maps on the Grand Canyon