A little over a year ago, I planted a couple seeds from a lemon. Today, I have a three saplings ranging from the size of seven to twelve inches. All three are currently in a 8"(w)x10"(l)x4"(h) pot. This is my fist attempt at something like this, so my intentions were just just to succeed at growing them and faintly with the bonsai process. As time goes on, I'm curious as to when I should begin the process of re-potting them, cutting the taproot, and combining them into one magnificent creation of my own. Also, is there any advice that can be offered to me? I'm looking for all I can get here.

Thanks