I hope you'll understand when I am not specific about certain things.
More than enough. I have redundancies in every weapons platform and have purchased based on establishing a layered protective perimeter from 1,500 yards. This means being able to reach out that far. Effective range is much less under stress. Most weapons are for close combat and designed for as much stealth as possible. Yes, this means I have NFA items. Calibers range, but I have tried to use calibers that can supply multiple weapons/platforms. Lets just say that my favorite calibers are .308, 5.56, .45, .380, 9mm, and .22lr. Some are all business, some are for training, then some are for fun.
I have multiple safes including one in each vehicle I own. A weapon is always in a safe when not on my person. I do not use trigger locks unless transporting a weapon that will not fit in a vehicle safe (long guns). Beyond that, a weapon never leaves the safe unless it is on me. Ammunition is stored separately, but at times in the same room/vehicle. Ammunition is maintained in a secure closet with locks on the ammo cans. When traveling, ammo is in locked cans. The only exception to this is the loaded magazine in the safe with my daily carry, which is close enough to deal with an intruder.
I only have one floor. You will too when you get old and your joints start barking at you when they sense stairs around.
No. Even when I receive an order of ammunition, as soon as I receive it the ammo is cataloged and immediately secured. If I exceed my current capacity to store in a secure manner, I order appropriate cans and locks to meet the new order.
If an intruder breaks in I can have my weapon out of the safe and loaded in less than 15 seconds (stress tested and trained), and many times less than 10 seconds. Again, this means there is a loaded magazine in the safe with an unloaded gun, so I just have to access the safe, grab the gun and the magazine, load the mag, and rack and roll.
That is what the desert is for.
Although the concept of having someone shooting at you while you train is suicidal. I would not condone such activity. There are training methods that can simulate battle stress and I recommend those than others that could put your life at risk.