Hi, I'm a former Californian and have ridden most of the coast.
I liked the K&S book, compared to using the ACA maps on the Lewis & Clark - the book has more info on side trips & sightseeing. Either will be fine for grades, distances & services - camping, food, bike shops, etc. And with either, you might want to supplement with AAA maps or the like for the major urban areas, or you'll be trapped on a little path of roads and won't be able to explore. Or just blow the map thing off and keep the ocean on your right.
With regard to timing, later is better for weather, earlier is better for crowds. You really don't have to worry about too hot on the coast, and later months are drier and have more consistent northwest wind. April/May is pretty early for the pacific northwest, plan to get a good amount of rain. June-August should be unrelentingly perfect (still bring rain gear), but everyone else will be out too, so you'll have more traffic.
Personally I would go in June or July, and just plan on not riding on the major holidays, and trying to ride early in the day on weekends. The only thing I would really time carefully is to not ride the Big Sur coast on a weekend - but that would be easy just hang out an extra day or two someplace fun a little north of there (SF, Santa Cruz, Monterey - all are nice).
If you are camping you should be OK with the crowds/campgrounds, but if you are hotelling that time of year plan to book rooms a few days in advance.
Have a lovely trip!