pressure does depend on the pipe you use... yes, but it depends mostly on the pump that will be driving it. Basically, the smaller diameter pipe you have, the higher pressure water you need to move the same volume of water through (just like higher resistance wire takes a higher voltage to drive the same current). Your 6mm pipe, with a low pressure pump will just slowly trickle out water, not in any misting form.
If instead you want a fine spray, you'd need a high pressure pump running through that small pipe (and then through some kind of misting nozzle) Kinda liek a windex bottle, I rmeember readign that those produce a fairly high pressure when you squeeze the trigger.
I'll get back to you about the sensors and LCD screen though, gotta get to work.