You should be able to use the Kanger clearomizers quite a few times each before changing out the heads. In fact, I haven't had to swap any out yet and I have been doing this 7 weeks. Generally speaking, if and when I have to clean them out because they seem to not be producing as good of vapor as they used to, I simply rinse them out really really well with hot water and let them dry out for a day or so, then fill them up and they have all just kept on working. That being said, if you need to replace the head, that part has the wick and the atomizer in it, which is the part that will eventually go bad. But you are right, all the Kangers already come ready to go - no need to purchase them and replacement heads unless you want to keep a couple on hand for "just in cases". As far as the liquid goes, I haven't tried anything off of Amazon, however, I just did a search and saw this sample pack: http://www.amazon.com/Hollywood-E-Liquid-BUY-WHOLESALE-Variety/dp/B007T09KKA/ref=sr_1_2?ie=UTF8&qid=1356523325&sr=8-2&keywords=e+liquid which does already contain the nic 18mg in it. This is the norm by the way, although you can purchase zero nic stuff from different places. The nicotine content is measured as milligrams of nicotine per milliliter of fluid and a teaspoon of fluid is roughly about 5 milliliters. Heavy smokers usually start out at high nicotine levels like 36 or 24 mg/ml, but 18 seems to be a pretty common mid-range level. You will notice more throatiness in fluids with #1 more nicotine and #2 more PG vs VG content. You will notice more vapor production with a higher VG content and, generally speaking, more flavor with more PG content. I hope that helps!