The most important part is it must remain dry. I leave it in the bag that it comes in, cutting only a smallish hole (an inch or so on diameter) which I keep clamped shut with a spring clamp.

In my main pantry I keep a 2qt container of the rice. When that container empties I go back and refill it again. I've had a bag last the better part of a year with no discernible loss and quality just by keeping it closed and climate controlled. In my bug out supplies I have a bunch of dry in mylar bags with oxygen absorbers. 3 years later they still taste exactly the same.

A $20, 25 lb bag has a little more than 50 cups of dry rice in it. Rice expands by a factor of 3 when you cook it.

A cup of cooked rice has little more than 200 calories with nothing in it. If I'm using as a main course, I plan for 1 and 1/2 to 2 cups per person, by the time you add seasonings and a reasonable amount of oil it brings it's not hard to get about a third of your daily calories out of a couple cups. You just have to be careful about nutrition because it doesn't have much.

So you could do 75 meals or maybe 150 sides out of a $20 bag of course paying for all the accoutrements to make it tasty.

Also of note stick to white rice for this. Brown rice still has the bran on it and a little bit of fat and tends to go bad faster. Also stay away from par-boiled rice, It cooks faster but it doesn't keep the same.

The other commenter gave a good rundown, but you don't have to get that scientific about it. I just use a large coffee mug to eyeball how much rice I want, and use the "finger method" to measure the rice to water ratio in the pot. Cook on high until boiling, cover and turn to medium for fifteen minutes, turn off heat and wait five minutes before uncovering and fluffing with a fork.

For storage I put the large coffee mug back in the rice bag, give it a twist and seal with a chip clip, and it's ready for the next time.

As to how long it lasts, that will depend on how much you eat and how big a bag you get. ;) But it will last you: a long time.