An August trip will mean hot temps and dry riding once you turn inland. However, it is certainly doable.
The headwinds have been "interesting" this year. Much more ocean breeze than normal IMO. I have a feeling that this will be changing though. If it doesn't change the headwinds will usually only be somewhere around 5-10kts. Good enough to sap 2-3 mph for an average rider but not "bad."
As for the "route" the Gaviota tunnel is narrow but there is a walkway you can use. After the tunnel the shoulder is plenty wide enough for safe riding. The climb is not that bad. There are a few nifty/neat places where you can just stop and rest if you need to. I do know that Hwy 1 to Lompoc is only part way up the hill so you don't have to do the whole 5 mile climb to Nojoqui. And the hill isn't as steep on the bottom half as it is near the top.
Lots of rollers north of Goleta on the 101. No water that I know of after El Capitan State Beach until the rest stop in Gaviota. But, umd might know of something that I don't. I'd be sure to fill up on water at the rest stop before leaving there because I'm pretty positive there is nothing on Hwy 1 until Lompoc.
Ventura to SB is a pretty well known route. Mapmyride should have it or you can follow the route for the Cool Breeze Century. (Use the route for the metric century that follows the coast to Carpinteria. Then either follow El Camino Real to Cabrillo to Las Positas to Modoc to Hollister OR take Foothill / Cathedral Oaks to Glenn Annie to Holister if you feel like lots of climbing and a few more miles.)
Most of all, enjoy your trip.