I'm guessing this itinerary is driven, at least in part, by friends and family along the route? Anyhow, a few thoughts:
Texas to southern California in the summer is insane. How many consecutive days of 100 degree heat can you tolerate? How much water and salt do you need to keep going? You might be able to do it, but it's hot and dry, and many of the snowbird services (restaurants, etc.) in the deserts are closed in summer, so you can't count on them for water. If your waypoints are fixed, I'd suggest starting later in the year, like August/September, to hit the southern part of your ride in October/November.
If you don't have to go through Memphis and Texas, I'd suggest heading west towards Montana and Washington, and then down towards California.
Since you're just starting bike touring, it'd be worth looking at Adventure Cycling maps (see
https://www.adventurecycling.org/routes-and-maps/adventure-cycling-route-network/interactive-network-map/ ). They're well worth the price - especially if you're planning to camp, since they'll help identify camping spots. You could cobble together a route from parts of the Northern Tier, Great Rivers South, Southern Tier, Route 66, and Pacific Coast routes that would solve 90% of your routing problems.
50 miles a day isn't a bad average overall. If you're planning to increase mileage above that, make sure you're packed very lightly, bikepacking style. There's some hills to get over, and they're not easy, particularly when you're loaded down.