First off, welcome to the other side!! I'm also a WDW vet who has spent the last 6 years traveling to the West Coast.
1) A car is NOT necessary, unless you wish to go run an errand, or if you're worried about time back to the airport; or if your hotel is way off site. It's also nice if you need to go make a Target run; eat somewhere away from Disney, etc. But again, a car really isn't necessary. If you get a hotel on property, or if you get one on Harbor, you'll be fine.
2) The park entrances literally face each other, with about 500 feet between them. Easy peasy. DTD is also right outside the park entrances.
3) Pirates at DL is quite different than the WDW version. We MUCH prefer the DL version.
4) Avengers Campus at Calif Adventure is nice, but not alot to do there. There are 2 rides currently (since they include what used to be the HTH, now rethemed for Guardians). Webslingers is pretty much a Marvel Toy Story Midway Mania.
5) If you can swing it, Carthay Circle restaurant is a VERY nice restaurant.
6) Def get at least one (1)
Genie+ for your party, so that you can have access to the Photopass pics.
7) Don't rush. There's ALOT of history at DL. Take the time to soak it up.
8) The crowds are definitely different (locals FAR outnumber visitors). They are very friendly (with the occasional exception...LOL)
9) DTD is MUCH MUCH smaller than Disney Springs.
10) Because of the proximity of the parks to the ocean, sometimes it can get breezy in the evenings. If that's the case, a light windbreaker or sweatshirt will be more than sufficient. If you don't want to pack one, but end up needing one, I know that the shop in Frontier Land sells actual wind breakers. Since you're going in June, it may not be an issue at all. So take this info with a grain of salt.
11) Get a locker if you plan on doing any shopping. Much better than lugging things around all day.
12) LOTS of QS locations with decent food. Use Mobile Ordering. It comes in VERY handy.
13) If you rope drop, you will get alot done during the first 2 hours or so at the parks. The locals really start packing the place about 10-11am. After that, all bets are off.
14) You should see World of Color.
15) Our first trip to DL, we focused on what you can't find at WDW. So that meant:
- Indiana Jones
- Pirates (because it's different)
- Avengers Campus
- Incredicoaster/Pixar Pier (be advised that this is much more a "carnival" feeling area)
- Matterhorn (very jolty - watch your back)
- Mr. Toad's Wild Ride
- Monster's Inc.
- Guardians Mission Breakout (HTH hotel)
- Radiator Springs Racers/CarsLand - Great theming (see it at night too)
16) If you're worried about all the sun, take a compact UV blocking Umbrella. Very handy.
17) Remember to breathe and have fun making family memories!!