JS100 tuning problems

Hi guys,
I think this forum is great but 1 problem is that all the info just overwhelms me that I don't know where to start!I guess being a good musician is just not enough specially in a country like the US where a guitar tech is almost more expensive than the instrument itself!
Well the reason I droped in was beacuse of my tuning probs on my JS 100.I was pretty impressed by the guitar when I bought it although there was a slight buzz on the open strings.The trouble started when I changed strings & I made a big mistake of changing all 6 together.Now I'm having lots of trouble with tuning.The tuning goes out of wack each time I lock the nut.I wonder if the nut has anything to do with it.I also removed & put back the bar behind the nut that holds the strings down.Is there any particular level it should be set? I understand the trem has to float paralel to the guitar surface but then the tremolo becomes too loose & moves fwd even at the slightest bend.Is there anyway I can keep the trmolo paralel & still keep it tight.There is a place for adjutment with the allan wrench at the lower side of the trem (from the backside of the guitar).I'm not sure what it does but will adjusting this help in anyway? If any of you guys can direct me to a page where I can find simple & clear answers on setting up the JS 100 that would help a lot.Thanks v much.