Hi...I'm new here, but I'll just jump in.
You said, "2- They list some oils twice from different countries. (ie. Essential Oil: Lavender, Water Soluble, Spain Essential Oil: Lavender, Bulgaria)"
It DOES make a difference about the origins of an oil. Their potency and even species vary based on where they come from. Remember that these things are all of an organic nature, so many things will affect their potency and overall quality.
BTW....I'd recommed the Lavender from Bulgaria.....it's a very nice scent and is one of the best that FNWL offers.
"How do I know which one is the right one?"
For the more common oils, such as lavender, you can't go too wrong, but if you start getting into the more obscure (ex. spikenard) or precious oils (rose or jasmine), I'd learn as much as I can about it. Please remember that these things are VERY potent and have serious affects on the body, both good and bad.
"3- What instruments are you using to measure these amounts when you mix them? A measuring cup or spoons or what?"
AND
"4- And is there a special kind of dropper that is used? When you say "drops" do you literally mean a drop of do you mean dropper fulls?"
LOL....a measuring cup? Essential oils are far too expensive and potent. Seriously tho, you measure EOs by the drop, they LITERALLY mean drops. Many of the more precious oils come in bottles that will distribute by the drop (most like this will say so in the description).....however, it's a good thing to buy a dropper or 2 that are dedicated to measuring out your oils. Many times, the oils will just come in bottles w/ a wide neck, so you'll need a dropper. They are available from FNWL and many other online places as well as health food stores. They cost anywhere from between $.50 and $1.50, depending on what size you get. For this, you'll probably only need a 1 oz dropper.
Buying a little bottle w/ a dropper included might be a good investment if you plan to work w/ essentail oil blends. They are handy for mixing them.
"5- Should I use this mixture instead of my daily Wild Growth Oil or Hot Six Oil? Or should I do it in addition?"
You can do either OR you can simply mix your essential oils into whatever carrier oil you already use and like. They'll only improve your existing product.
"6- Is this something to be used every night or once a week?"
It all depens on how you wear your hair now...processed-unprocessed, braided-dreded, etc.... depends on if you like/need a bit of oil in your hair and how often.
IMHO, there's no problem if you choose a daily application or however often you find/desire necessary.