If you buy (or trade for) seeds, they are fairly easy to grow. Make sure you sand or knick on side of the seed, to get through the hard exterior...and just plop them in water. In about a week, you will see the sprout coming out. Make sure you constantly change the water or you will end up with a nasty fungus blob. Soon a leaf will make it's way to the surface of the water. At that point, you can plant the seed/plant and get them ready for the pond.
No, it will not get as large the first year as a tuber...but will get big and leafy if treated right. I've only had one smaller version bloom the first year, so I'm not sure about the big ones. If you can find a tuber (and it must have a growing tip) it will get you off to a faster start. Although a large tubby fully of lotus leaves up on their tall stems is equally elegant, even without the blooms.