DSP&P grade along the South Platte, drive from Pine-South Platte-Deckers-Woodland Park is nice. One can hike into the lower lower part of the canyon from South Platte too. (as mentioned here recently, you can hike in from the Waterton end too. ).
As to hiking, it's only going to be May so wear layers and leave space in your daypack to switch them on and off. If it's nice when you start out, carry the extra layers, the weather can turn on a dime and that extra sweatshirt, pair of gloves, stocking cap, etc can be suddenly needed. Even vital if you go high enough.
Hank