There's a lot more to know than can be explained in a "tell me what I need" thread..... I did a year's worth of research before finally pulling the trigger on my nano. Best place to start is in the "Nano Reefs" section of this forum and begin reading everybody's build threads. You will get an idea of what to do (and not do) while getting going.
Read, read, read until your eyes bleed, and then read some more...... Search the forum & 'net when you have specific questions. If you can't find an answer, then don't hesitate to ask.