:iagree: Expect cold nights, possibly dipping below freezing, but warming up very quickly during the day. This is the time of the year where you will use both heat and A/C!
Nice thing about Moab is that some of the "easy" trails are also the most scenic. Potash Road will take you out of Moab and runs along the Colorado River where you can either turn off at Long Canyon or continue on until you hit the beginning of White Rim Trail.
At White Rim you can either drive down until you feel like turning around, or you can take a right and go up the Shaffer Trail switchbacks to the top of the plateau for some awesome views.
White Rim Trail is 100 miles long, I wouldn't try to do it in a day (although many people do, IMO it doesn't give you time to really enjoy it.) Sounds like you aren't camping so if I was you, I'd probably just go down White Rim a few miles to some of the great overlooks and then turn around and go back up to the top of Island in the Sky. There are lots of paved roads up there that lead to awesome views as well. You could also hit Gemini Bridges, another easy trail with great views.
I'll also second the Charles Wells book. It's a great, handy little guidebook to have.
In truth, there's not a "bad" time to be in Moab, but IMO Spring and Fall are the best time to be there!