15w-40 should be fine for you in California, unless maybe you are up on top of a hill somewhere where you'll see cold temps.
For reasons nobody can really explain, Shell Rotella works fine but tends to have the engine "drink" about a quart or two between change intervals. Conversely, Chevron Delo seems to remain at the same level on the dipstick longer. You can of course always go to synthetic oil, but keep in mind that IDIs tend to leak (some more than others, but they all leak some) and synthetic oil typically increases any leaks.
No matter which way you end up going, you can consider running the larger 7.3 Powerstroke FL-1995 oil filter. It holds an additional quart of oil and has more dirt holding capability than the standard IDI filter.
Good luck and welcome aboard.