Agreed that the WDW Veterans thread is an absolute must-do starting point for this scenario.
That said, a few comments specific to this group and itinerary...
In June they begin Downtown Disney demolition and construction on the fourth luxury hotel for Disneyland, and it will take over the west end of Downtown Disney by the Disneyland Hotel. By February'19 that area will be leveled, but it will make walking into the parks from the Disneyland Hotel difficult and the monorail station may be closed.
With a child who has Cars Land at the top of their list, it would be wise to budget the extra money to stay at the Grand Californian instead of the Disneyland Hotel in February '19.
I always recommend people look at Disneyland via Google Earth, and that gets you a better idea of how the place fits together. And remember, there are nearly as many rides and attractions and major entertainment spectaculars crammed into these two parks the size of Epcot as there are in all four WDW theme parks combined. Lines are typically shorter at Disneyland Resort because of this, and rides can literally be stacked on top of one another or have entrances just a few yards from each other. MaxPass can still be very handy when it comes to grabbing Fastpasses for the popular E Tickets like Radiator Springs Racers, Indiana Jones, Guardians of the Galaxy, etc.
Same Scale and Same Size. Very different land use.