Clones take about 3 weeks to build a good root system and start growing. Many don't even count this 3 weeks, but I suggest if you have not used clones before, that you budget for it.
You may well be familiar, I am just posting for other people that are new, or new to clones.
I think I understand what you want to do better now. You could make one 3x3 tray filled quite densely, you could try 12 even as you want to grow small fast plants. Personally, I prefer a bit of vegging, but, I am also running a near 100 plant SOG at the moment. Sometimes situations change our demands and needs.