Hi!

I'm just learning myself, but I think I might be able to point you in the right direction...

1) No major issues with larger than needed pots. Your tree will have room to grow, and in the long term if that's what you're looking for you'll be fine. Just 2 words of caution. First make sure that you are watering evenly. With a small rootball to soil ratio its harder to keep the soil evenly moist. This can be limited by using gritty or even 5-1-1 but you still have to be concerned with the mix going hydrophobic from lack of water. Also, if something is wrong with your trees it may be necessary to see what's happening with the roots. This could be tough to pull off if you're using huge containers.

2) Gritty and 5-1-1 are both great. I use both, and definitly prefer the gritty for citrus here in New England, as during the winter it really prevents over-watering. However, its heavy as sin and can get pricy. If you're using big pots you will need a lot of mix, meaning it'll be difficult to move your pots. The 5-1-1 can be just as effective (I have plants that are very happy in that mix), and in the California sun you'll probably not have to worry about over-watering as much.

3) Most people here recommend exactly what you've proposed for a feeding schedule. Check out MeyerMike's plants in a forum search to see the great results he's getting with the same regimen.

4) I'd kill for your zone for so many reasons. You can keep them outside just as you would your in-ground citrus. Bring it in when the temps get below freezing (does that even happen in sunset 17??)

5) Container plants can be fickle, but most people kill them with kindness. Don't overwater them or move them around from shady to sunny conditions rapidly. Just give them a quick soaking every few days and you'll be fine!