395 is an absolutely beautiful drive with many campgrounds along the way. That early in the season you won't have a difficult time getting a site without reservations.
You said you want to go to Yosemite, Sequoia and Kings Canyon. You can't get to Sequoia/Kings Canyon from 395. You'd have to go around to the other side of the mountains - around Fresno.
For Yosemite from 395 you'd be taking the highway from Lee Vining (120 and Tioga Pass). Keep a watch on the national park's site for road opening for 120. It's closed for snow right now.
https://www.nps.gov/yose/planyourvisit/tiogaopen.htmOn 395 south of Lee Vining is the June Lake area with some very nice scenic forest service campgrounds - via the paved June Lake Loop road.
Further south be sure to stop in Lone Pine on 395. Interesting movie history in the area.
