About weight ratios; the first number indicates the weight during start up. If its 10w-30, its weight will be a 10 on start up. The second number indicates the weight of the oil at operating temperature. Since you live in a hotter climate, you should be fine with 10w-30.
I would just use 6 qts of Mobil 1. I say six, because although the motor takes 5, I would use some(not all) of the extra qt. to fill the oil filter up before installing it. This helps to reduce friction during start up after an oil change. All in all, it should take about 5.2-5.3qts. You can keep what is left over from the extra qt. around just in case if you ever need it.
Mobil 1 is a synthetic motor oil and already contains any additive packages Lucas Oil stabalizer would have. As said above, if you're not having any leaks or issues, no sense in using any extra additives. Most of them are snake oil anyways.
I personally use Amsoil 5w-30 High performance motor oil with an Amosil oil filter. I like it. I only have to change my oil once a year. I just recently changed it after 1 year of use, and it came out looking almost new. No sign of dirt or foul build up to be seen.