Amy, sounds like a fine ride. I have done a bunch of it, the northern part. You mention taking Highway 25 east of Pinnacles. Be prepared for very little water and surprising hills. If you take Gloria Road over to the Salinas Valley, you will be climbing a lot with no water sources that I can remember, but it is a beautiful route. As an aside, although bikes are not allowed to ride through Pinnacles, the eastern entrance road will take you most of the way to the Balcony Caves trail and there is an easy walk around the caves for horse folk. Not saying walking it with your packs carried on a wheeled support beside you is strictly legal, but I know it can be done <G>. You will have to carry your bike over some water courses and up and over a few rocky sections.
The Arroyo-Seco - Indians road does have some water. There is another recent conversation on this same topic. For someone coming from the north who has to take the dirt backroad to FHL, the turnoff is a few miles from the Indians, a sharp left turn up a small ridge. It is a nice, all-weather road along the eastern side of the valley that was, I think, the only route when I rode it first in 1964.
You should have a great ride. The flowers will be brilliant.