The only way I'd be concerned about the amount of LR you have is if you have no substrate below it. If you have a few inches of sand or CC, you will have no problems with any amount of LR in your tank. The tanks can handle a lot of abuse in this way.
Cured LR means that there is no dead and decaying material in it. Some of the life in and on the LR dies off during the time the rock leaves the ocean and the time it enters your tank. The decay of all these animals is what causes your tank to go through a mini-cycle when you add un-cured LR. Therefore, cured LR is rock that has sat around long enough in a tank to have already gone through all the die off, and all that remains is alive animals. However, usually there is less diversity of life on cured LR because seldom is it cured in ideal conditions for the animals to live. By curing the rock yourself, you can take the extra steps to make sure as much of the life on the rock stays alive as possible. Therefore, cured LR is easier to work with, but IME, you will end up with better LR if you get un-cured and cure it yourself. This can be done in the tank gradually, if you have fish and animals in the tank already. Or you can put all the LR you will need in the tank at once and let the die off of the LR cycle your tank before you add any other animals. Or you can cure the LR in a separate tank or tub (large rubbermaid containers work well). All you have to do is drop a heater and a powerhead into the tank, and maybe a skimmer into the tank or tub and you can cure the rock yourself. That is the method I used. Also, I would take about a piece a day from the curing tub and add it to the main tank (since I already had animals in my display tank). This way I was able to save money by buying all the LR at once, I was able to cure it myself, and I was able to keep more of the life on the LR alive because I was able to essentially speed up the curing time by taking a piece a day out of the curing tub and into the display tank.