>>I read that they should be fed no more than they can eat in one sitting(15 mins.) Does that mean to take any extra food out 15 mins. after putting the food in?
Yes, if the prey is crickets. Crickets can bite if left in the cage. But, if you feed mealworms, they can be contained in a bowl. Both are better than one or the other.
>>I also read that they should be offered pure calcium twice a week. Is pure calcium the same as calcium carbonate or just calcium w/o vitamin D3?
The calcium you should use is calcium carbonate with vitamin D3. The D3 helps in the absorption of the calcium
>>And last I read to offer it a multi vitamin once a week. What is a multi vitamin?
A multi vitamin is a suplement like calcium. You sprinkle it on the insects to provide extra nutrition. As hatchlings and juveniles the multi vitamin is not as neccesarry as the calcium. They are growing very quick and need alot of protein and calcium for bone growth.
I would recommend leaving a dish of calcium in the cage all the time. Leos do eat the calcium if they need it. I would also put mealworms in this same dish. As for the multi vitamin, once or twice a week should be good throughout your geckos life.