Matt,
Welcome to apple world
I had a large one for quite a while. I loved it. It was too much work. I sold it... I wish I hadn't. Apples are truly wonderful bonsai. Yours is very nice.
Below are some of the things that I learned with my apple:
You may have issues with not having enough cold for apple in So. Cal. If this is a locally grown variety, it may not be a problem. Most apples need a very cold dormancy to fulfill their genetic chilling requirement. If they don't get it, they are cranky.
Expect every kind of leaf eating and trunk eating pest in the neighborhood to make a visit to your new tree. Apple is a bug and fungus magnet. Borers and aphids are particularly troublesome, as are wooly adelgids.
Exposed deadwood on apples is almost always attacked by whatever borer species is in your area. Watch for the signs.
Preventative spraying of a broad spectrum fungal solution, as well as a wide ranging bug killer at the beginning middle and end of the growing season helps.
Apples are extremely cold tolerant. Frost will not affect leaf or flower buds, but frost will burn growth that has extended. Keep an eye out for it. Bring the tree in when it's in the forecast. A failure to do this will result in black dead leaves for a month until they're replaced.
For what it's worth, flowering on apples is highly variable and depends on specialized pruning. Takes some getting used to. Also flowering branches and resulting fruit should be thinned. Failure to thin fruit, in particular, can result in death of the fruiting branch.