my first plant

So while in the process of getting my medical card, i started setting up my grow room and buying equipment. While i further invest my money and time into the making my room better i decided to plant a few seeds. I bought a book and did my research from there. Right now I am just sort of getting used to growing, and taking my time making my grow room an optimal growing area for my next and first real garden. Right now though i do have these two plants. One is a seedling, the other is about 8 inches tall, i will put pictures bellow. The plants themselves sit under a 400 watt HPS sun system with a metal halide conversion bulb for this part of the grow. They are on a 6/18 light cycle, with just a few simple fans moving air for now. I will have ventalating when i set up my hydroponic system. The plants are also being slowly put onto nutrients. The big plant is being fed the nutrient solution ( I bought a nice starter kit with good solutions that also have stages for each set of growth, and the pH levels are easy). The little plant is just getting pure water and ocassionally some transplanting nutrients for root develpment. This is my first grow though and will take any advice for a low budget simple grow like this. What im really wondering about is topping and pruning. When should i start doing that, like whats a good size to start that? Any tips on that would be much appreciated. Here is a picture.

To top you need to have at least 5 or 6 internodes

also looks like water drops on leaves in pic, not good under that light as can cause burns
drops act like a magnifier and cause hot spots

don't top the plant ,you can bend the plant when it gets big. i don't like to top m