Well, this year you may find you are early for wildflowers. Because of a lousy, cold spring there is still plenty of snow covering the high meadows currently. May not get much of a show until August.
You'll find the meadows at Paradise to be some of the closest to the campground you're staying at, and may be the best for wildflowers depending on the season. There are plenty of creeks and falls in the area: Edith, Christine, Comet, to name a few. Check the visitor centers at either Longmire or Paradise for maps and trail info. Farther away from you, the western part of the mountain including Eunice Lake and Spray Park are good with great fields of flowers.
One thing you will find is that in the Paradise area you're actually on the lower slopes of the mountain, so it will loom large in your photographs, maybe too much so depending on your tastes. If you travel to, say, the Sunrise area on the eastern side, you'll find vistas that include more of the landscape.
Probably the most photographed view is from Reflection Lake, not far from where you'll be camped. For that reason I usually avoid it like the plague.
Anyway, have fun and I hope the weather cooperates. Like most big mountains, Rainier makes its own, and three days is kind of pushing your luck, even in the summer - not unusual to go days or weeks socked in with clouds.