When I started diy I did as suggested and mixed single flavor recipes. For the most part I was disappointed with this. I then started mixing multi-flavored juices and I haven't looked back. I can't tell you that you should skip the single flavor mixes as that is definitely part of the learning curve. What I can say is that you are going to need a lot more flavors if you are really going to jump in with both feet. I think I have over 100 bottles myself and am always looking to find more. Yes - I am addicted to
vaping on all levels. Check these out to get an idea of what flavors are used all the time in mixes: ie. vanilla custard, sweet cream, etc.
E-Liquid Recipes | DIY E-Juice | e cig Liquids diyRecipeBook. There are more sites than these out there for recipes. In regards to measuring tools I use syringes exclusively. I have 1ml, 3ml, 5ml and 10ml. I do as others have mentioned and do not always put nicotine, which is expensive, in test batches. I usually make a 5ml test batch so I have enough to mess around with. I am not particularly fond of steeping as I have had more flavors I like immediately which lose flavor after steeping.

And lastly - HAVE FUN